Biomedical subjects

Bruce D Walker

Publications and source records attributed to Bruce D Walker.

At least 37 records · Page 2Linked to original sources

PubMed2006

Longitudinal analysis of clinical markers following antiretroviral therapy initiated during acute or early HIV type 1 infection.

BACKGROUND: Treatment of acute human immunodeficiency virus type 1 (HIV-1) infection may have unique immunologic, virological, and clinical benefits. However, the timing of treatment, optimal starting regimens, and expected response to therapy have not been defined.Methods. One hundred two subjects treated during acute and early HIV-1 infection were observed prospectively to determine the effect of time elapsed before initiation of therapy on time to virological suppression and absolute CD4+ cell count. Subjects were divided into pre- and postseroconversion groups on the basis of HIV-1 antibody status at the time of initiation of treatment. Absolute CD4+ cell counts were compared between these groups and with those of historical untreated persons who had experienced seroconversion. Potential predictors of time to virological suppression and CD4+ cell count at > or =12 months were assessed. RESULTS: Ninety-nine (97%) of 102 subjects achieved virological suppression. The median time to suppression was 11.1 weeks (95% confidence interval, 9.4-14.9) and was independent of initial regimen. The mean CD4+ cell count at 12 months was 702 cells/mm3 (95% confidence interval, 654-750 cells/mm3) and showed an increasing trend over 60 months. Treated subjects demonstrated a statistically significant gain in the CD4+ cell count, compared with untreated historical control subjects, at > or =12 months. Comparable virological and immunologic outcomes were seen in the pre- and postseroconversion groups. Baseline virus load and nadir CD4+ cell count predicted time to virological suppression and CD4+ cell count at > or =12 months, respectively. CONCLUSIONS: Early treatment of HIV-1 infection is well tolerated and results in rapid and sustained virological suppression. Preservation of CD4+ cell counts may be achieved with early therapy, independent of seroconversion status. Protease inhibitor-based and nonnucleoside reverse-transcriptase inhibitor-based regimens show comparable performance in tolerability, time to virological suppression, and CD4+ cell count when used as a first regimen.

Acquired Immunodeficiency Syndrome↗

PubMed2006

Association between HIV Type 1-specific T cell responses and CD4+ T cell counts or CD4+:CD8+ T cell ratios in HIV Type 1 subtype B infection in China.

CD4+ T cell counts and CD4+:CD8+ T cell ratios represent key determinants of HIV disease progression and infectivity. However, the relationship between the HIV-1-specific cytotoxic T lymphocyte (CTL) response and these determinants has not been elucidated for all HIV-1B and HIV-1C proteins. In the present study, virusspecific T cell responses to HIV-1B and HIV-1C proteins were analyzed with interferon gamma (IFN-gamma) enzyme- linked immunospot (ELISpot) assays using synthetic overlapping peptides corresponding to naturally occurring HIV-1B and HIV-1C consensus sequences. For Gag/Gag p24/Gag p17, a correlation between T cell responses and CD4+ T cell count in HIV-1 clade B and clade C was seen: elevated T cell response resulted in higher CD4+ T cell production. A statistically significant correlation between the Pol-specific T cell response and CD4+ T cell counts was also found in HIV-1 subtype C. For all HIV-1B and HIV-1C proteins, a correlation between the HIV-1-specific T cell response and CD4+:CD8+ T cell ratios was found for Tat and Pol proteins. CD4+ T cell counts in patients with Tat and/or Rev T cell response were higher than in patients without Tat and/or Rev T cell response. We suggest that this correlation within HIV-1B and HIV-1C Gag p24/Gag p17 responses makes the Gag p24/Gag p17 region a potential vaccine candidate and that HIV-1-specific CTL epitopes toward Pol are important in controlling HIV-1 infection; we emphasize that future vaccination strategies should include these early antigens, Tat and Rev.

Adolescent↗

PubMed2006

Infection of CD127+ (interleukin-7 receptor+) CD4+ cells and overexpression of CTLA-4 are linked to loss of antigen-specific CD4 T cells during primary human immunodeficiency virus type 1 infection.

We recently found that human immunodeficiency virus (HIV)-specific CD4+ T cells express coreceptor CCR5 and activation antigen CD38 during early primary HIV-1 infection (PHI) but then rapidly disappear from the circulation. This cell loss may be due to susceptibility to infection with HIV-1 but could also be due to inappropriate apoptosis, an expansion of T regulatory cells, trafficking out of the circulation, or dysfunction. We purified CD38+++CD4+ T cells from peripheral blood mononuclear cells, measured their level of HIV-1 DNA by PCR, and found that about 10% of this population was infected. However, a small subset of HIV-specific CD4+) T cells also expressed CD127, a marker of long-term memory cells. Purified CD127+CD4+ lymphocytes contained fivefold more copies of HIV-1 DNA per cell than did CD127-negative CD4+ cells, suggesting preferential infection of long-term memory cells. We observed no apoptosis of antigen-specific CD4+ T cells in vitro and only a small increase in CD45RO+CD25+CD127dimCD4+ T regulatory cells during PHI. However, 40% of CCR5+CD38+++ CD4+ T cells expressed gut-homing integrins, suggesting trafficking through gut-associated lymphoid tissue (GALT). Furthermore, 80% of HIV-specific CD4+ T cells expressed high levels of the negative regulator CTLA-4 in response to antigen stimulation in vitro, which was probably contributing to their inability to produce interleukin-2 and proliferate. Taken together, the loss of HIV-specific CD4+ T cells is associated with a combination of an infection of CCR5+ CD127+ memory CD4+ T cells, possibly in GALT, and a high expression of the inhibitory receptor CTLA-4.

ADP-ribosyl Cyclase 1↗

PubMed2006

Relative dominance of Gag p24-specific cytotoxic T lymphocytes is associated with human immunodeficiency virus control.

Conflicting data on the role of total virus- and protein-specific cytotoxic-T-lymphocyte (CTL) responses in the control of human immunodeficiency virus (HIV) disease progression exist. We present data generated from a Peruvian cohort of untreated, clade B-infected subjects, demonstrating that the proportion of Gag-specific, and in particular p24-reactive, CTL responses among the total virus-specific CTL activity is associated with individuals' CD4 counts and viral loads. Analyses in a second cohort in the United States confirm these findings and point towards a dominant role of Gag-specific immunity in effective control of HIV infection, providing important guidance for HIV vaccine development.

CD4 Lymphocyte Count↗

PubMed2006

Fitness cost of escape mutations in p24 Gag in association with control of human immunodeficiency virus type 1.

Mutational escape by human immunodeficiency virus (HIV) from cytotoxic T-lymphocyte (CTL) recognition is a major challenge for vaccine design. However, recent studies suggest that CTL escape may carry a sufficient cost to viral replicative capacity to facilitate subsequent immune control of a now attenuated virus. In order to examine how limitations can be imposed on viral escape, the epitope TSTLQEQIGW (TW10 [Gag residues 240 to 249]), presented by two HLA alleles associated with effective control of HIV, HLA-B*57 and -B*5801, was investigated. The in vitro experiments described here demonstrate that the dominant TW10 escape mutation, T242N, reduces viral replicative capacity. Structural analysis reveals that T242 plays a critical role in defining the start point and in stabilizing helix 6 within p24 Gag, ensuring that escape occurs at a significant cost. A very similar role is played by Thr-180, which is also an escape residue, but within a second p24 Gag epitope associated with immune control. Analysis of HIV type 1 gag in 206 B*57/5801-positive subjects reveals three principle alternative TW10-associated variants, and each is strongly linked to concomitant additional variants within p24 Gag, suggesting that functional constraints operate against their occurrence alone. The extreme conservation of p24 Gag and the predictable nature of escape variation resulting from these tight functional constraints indicate that p24 Gag may be a critical immunogen in vaccine design and suggest novel vaccination strategies to limit viral escape options from such epitopes.

Alleles↗

PubMed2006

HLA Alleles Associated with Delayed Progression to AIDS Contribute Strongly to the Initial CD8(+) T Cell Response against HIV-1.

BACKGROUND: Very little is known about the immunodominance patterns of HIV-1-specific T cell responses during primary HIV-1 infection and the reasons for human lymphocyte antigen (HLA) modulation of disease progression. METHODS AND FINDINGS: In a cohort of 104 individuals with primary HIV-1 infection, we demonstrate that a subset of CD8(+) T cell epitopes within HIV-1 are consistently targeted early after infection, while other epitopes subsequently targeted through the same HLA class I alleles are rarely recognized. Certain HLA alleles consistently contributed more than others to the total virus-specific CD8(+) T cell response during primary infection, and also reduced the absolute magnitude of responses restricted by other alleles if coexpressed in the same individual, consistent with immunodomination. Furthermore, individual HLA class I alleles that have been associated with slower HIV-1 disease progression contributed strongly to the total HIV-1-specific CD8(+) T cell response during primary infection. CONCLUSIONS: These data demonstrate consistent immunodominance patterns of HIV-1-specific CD8(+) T cell responses during primary infection and provide a mechanistic explanation for the protective effect of specific HLA class I alleles on HIV-1 disease progression.

Acquired Immunodeficiency Syndrome↗

PubMed2006

Impaired hepatitis C virus-specific T cell responses and recurrent hepatitis C virus in HIV coinfection.

BACKGROUND: Hepatitis C virus (HCV)-specific T cell responses are critical for spontaneous resolution of HCV viremia. Here we examined the effect of a lymphotropic virus, HIV-1, on the ability of coinfected patients to maintain spontaneous control of HCV infection. METHODS AND FINDINGS: We measured T cell responsiveness by lymphoproliferation and interferon-gamma ELISPOT in a large cohort of HCV-infected individuals with and without HIV infection. Among 47 HCV/HIV-1-coinfected individuals, spontaneous control of HCV was associated with more frequent HCV-specific lymphoproliferative (LP) responses (35%) compared to coinfected persons who exhibited chronic HCV viremia (7%, p = 0.016), but less frequent compared to HCV controllers who were not HIV infected (86%, p = 0.003). Preservation of HCV-specific LP responses in coinfected individuals was associated with a higher nadir CD4 count (r(2) = 0.45, p < 0.001) and the presence and magnitude of the HCV-specific CD8(+) T cell interferon-gamma response (p = 0.0014). During long-term follow-up, recurrence of HCV viremia occurred in six of 25 coinfected individuals with prior control of HCV, but in 0 of 16 HIV-1-negative HCV controllers (p = 0.03, log rank test). In these six individuals with recurrent HCV viremia, the magnitude of HCV viremia following recurrence inversely correlated with the CD4 count at time of breakthrough (r = -0.94, p = 0.017). CONCLUSIONS: These results indicate that HIV infection impairs the immune response to HCV-including in persons who have cleared HCV infection-and that HIV-1-infected individuals with spontaneous control of HCV remain at significant risk for a second episode of HCV viremia. These findings highlight the need for repeat viral RNA testing of apparent controllers of HCV infection in the setting of HIV-1 coinfection and provide a possible explanation for the higher rate of HCV persistence observed in this population.

CD4-Positive T-Lymphocytes↗

PubMed2005

Control of human immunodeficiency virus replication by cytotoxic T lymphocytes targeting subdominant epitopes.

Despite limited data supporting the superiority of dominant over subdominant responses, immunodominant epitopes represent the preferred vaccine candidates. To address the function of subdominant responses in human immunodeficiency virus infection, we analyzed cytotoxic T lymphocyte responses restricted by HLA-B*1503, a rare allele in a cohort infected with clade B, although common in one infected with clade C. HLA-B*1503 was associated with reduced viral loads in the clade B cohort but not the clade C cohort, although both shared the immunodominant response. Clade B viral control was associated with responses to several subdominant cytotoxic T lymphocyte epitopes, whereas their clade C variants were less well recognized. These data suggest that subdominant responses can contribute to in vivo viral control and that high HLA allele frequencies may drive the elimination of subdominant yet effective epitopes from circulating viral populations.

AIDS Vaccines↗

PubMed2005

Fluctuations of functionally distinct CD8+ T-cell clonotypes demonstrate flexibility of the HIV-specific TCR repertoire.

T-cell receptor (TCR) diversity of virus-specific CD8+ T cells likely helps prevent escape mutations in chronic viral infections. To understand the dynamics of the virus-specific T cells in more detail, we followed the evolution of the TCR repertoire specific for a dominant HLA-B*08-restricted epitope in Nef (FLKEKGGL) in a cohort of subjects infected with HIV. Epitope-specific CD8+ T cells used structurally diverse TCR repertoires, with different TCRbeta variable regions and with high amino acid diversity within antigen recognition sites. In a longitudinal study, distinct Vbeta populations within the HIV-specific TCR repertoire expanded simultaneously with changes in plasma viremia, whereas other Vbeta populations remained stable or even decreased. Despite antigenic variation in some subjects, all subjects had the consensus sequence present during the study period. Functional analysis of distinct Vbeta populations revealed differences in HIV-specific IFN-gamma secretion ex vivo as well as differences in tetramer binding, indicating functional heterogeneity among these populations. This contrasts with findings in a subject on antiretroviral therapy with suppression of viremia to less than 50 copies/mL, where we observed long-term persistence of a single clonotype. Our findings illustrate the flexibility of a heterogeneous HIV-1-specific CD8+ TCR repertoire in subjects with partial control of viremia.

Adult↗

PubMed2005

Expansion of HIV-specific CD4+ and CD8+ T cells by dendritic cells transfected with mRNA encoding cytoplasm- or lysosome-targeted Nef.

Transfection with synthetic mRNA is a safe and efficient method of delivering antigens to dendritic cells for immunotherapy. Targeting antigens to the lysosome can sometimes enhance the CD4+ T-cell response. We transfected antigen-presenting cells (APCs) with mRNA encoding Gag-p24 and cytoplasmic, lysosomal, and secreted forms of Nef. Antigen-specific cytotoxic T cells were able to lyse the majority of transfected targets, indicating that transfection was efficient. Transfection of APCs with a Nef construct bearing lysosomal targeting signals produced rapid and prolonged antigen presentation to CD4+ and CD8+ T cells. Polyclonal CD4+ and CD8+ T-cell lines recognizing multiple distinct epitopes were expanded by coculture of transfected dendritic cells with peripheral blood mononuclear cells from viremic and aviremic HIV-infected subjects. Importantly, lysosome-targeted antigen drove a significantly greater expansion of Nef-specific CD4+ T cells than cytoplasmic antigen. The frequency of recognition of CD8 but not CD4 epitopes by mRNA-expanded T cells was inversely proportional to sequence entropy and was similar to ex vivo responses from a large chronic cohort. Thus human dendritic cells transfected with mRNA encoding lysosome-targeted HIV antigen can expand a broad, polyclonal repertoire of antiviral T cells, offering a promising approach to HIV immunotherapy.

CD4-Positive T-Lymphocytes↗

PubMed2005

Antagonism of HIV-specific CD4+ T cells by C-terminal truncation of a minimum epitope.

Antagonism of T cell responses by variants of the cognate peptide is a potential mechanism of viral escape from immune responses and may play a role in the ability of HIV to evade immune control. We show here a rarely described mechanism of antagonism by a peptide shorter than the minimum length epitope for an HIV p24-specific CD4+ T cell clone. The shorter antagonist peptide-MHC complex bound the T cell receptor (TCR), albeit with lower affinity than the full-length agonist peptide. Prior work showing the crystal structure of the peptide-MHC complex revealed a unique glycine hinge near the C-terminus of the agonist peptide, allowing the generation of full-length antagonist peptide lacking the hinge. These results confirm the dependence of productive TCR engagement on residues spilling out from the C-terminus of the MHC binding groove and show that partial engagement of the TCR with a truncated, low-affinity ligand can result in T cell antagonism.

Amino Acid Sequence↗

PubMed2005

Diagnosis of unexplained cardiac arrest: role of adrenaline and procainamide infusion.

BACKGROUND: Cardiac arrest with preserved left ventricular function may be caused by uncommon genetic conditions. Although these may be evident on the ECG, long-term monitoring or provocative testing is often necessary to unmask latent primary electrical disease. METHODS AND RESULTS: Patients with unexplained cardiac arrest and no evident cardiac disease (normal left ventricular function, coronary arteries, and resting corrected QT) underwent pharmacological challenge with adrenaline and procainamide infusions to unmask subclinical primary electrical disease. Family members underwent noninvasive screening and directed provocative testing on the basis of findings in the proband. Eighteen patients (mean+/-SD age, 41+/-17 years; 11 female) with unexplained cardiac arrest were assessed. The final diagnosis was catecholaminergic ventricular tachycardia (CPVT) in 10 patients (56%), Brugada syndrome in 2 patients (11%), and unexplained (idiopathic ventricular fibrillation) in 6 patients (33%). Of 55 family members (mean+/-SD age, 27+/-17 years; 33 female), 9 additional affected family members were detected from 2 families, with a single Brugada syndrome patient and 8 CPVT patients. CONCLUSIONS: Provocative testing with adrenaline and procainamide infusions is useful in unmasking the etiology of apparent unexplained cardiac arrest. This approach helps to diagnose primary electrical disease, such as CPVT and Brugada syndrome, and provides the opportunity for therapeutic intervention in identified, asymptomatic family members who harbor the same disease.

Anti-Arrhythmia Agents↗

PubMed2005

Differential targeting and shifts in the immunodominance of Epstein-Barr virus--specific CD8 and CD4 T cell responses during acute and persistent infection.

The evolution of Epstein-Barr virus (EBV)-specific T cell responses that occurs during the acute and persistent stages of infection remains poorly characterized despite its importance for developing immune interventions for EBV-associated disorders. This study assessed T cell responses to 113 EBV-derived epitopes in 40 subjects with acute or persistent EBV infection. Although no significant differences were seen in the breadth of CD8 and CD4 T cell responses, their magnitude differed significantly over time; acutely infected subjects generated especially strong responses to lytic viral antigens. The cross-sectional shift in immunodominance was also confirmed in subjects followed longitudinally from acute to persistent infection. In addition, human leukocyte antigen-matched siblings with discordant histories of symptomatic EBV infection showed no significant differences in their response patterns, suggesting that symptomatic EBV infection does not lead to unique persistent-stage responses. These data provide an assessment of immunodominance patterns and guidance for developing immunotherapeutic interventions for EBV-associated disorders.

Amino Acid Sequence↗

PubMed2005

High degree of inter-clade cross-reactivity of HIV-1-specific T cell responses at the single peptide level.

OBJECTIVES: To determine HIV-1-specific T cell responses in clade B infected individuals recognizing the clade A, B and C consensus sequences in order to assess the degree of inter-clade cross-reactivity of these immune responses at the single epitope level. METHODS: HIV-1-specific T cell responses were assessed cross-sectionally in 27 chronically HIV-1-infected individuals from a population infected mainly with clade B viral strains, using an interferon-gamma Elispot assay with a total of 1230 overlapping peptides spanning the entire amino acid sequence of the clade A, B and C 2001 consensus sequences. RESULTS: No significant difference was observed between the total magnitude or breadth of T cell responses recognizing either the clade A, B or C consensus sequences. However, at the single peptide level, 194 T cell responses were identified that recognized only one of the three different clade-specific peptide variants (A: B: C, 34: 105: 55), 125 T cell responses recognized two of the three peptide variants (AB: AC: BC, 71: 15: 39) and 166 T cell responses (34%) were cross-reactive with all three different peptide variants. Peptides recognized in all three consensus sequence variants had a significantly lower entropy (P < 0.0001) and a significantly higher inter-clade homology (P < 0.0001). CONCLUSIONS: Viral epitopes within regions of low HIV-1 clade B diversity and high inter-clade homology can be recognized in the clade A, B and C variants and indicate a wide degree of cross-isolate and cross-clade recognition by HIV-1-specific T cells. These regions may therefore be of particular relevance for the design of HIV-1 vaccines.

Adult↗

PubMed2005

Use of a novel GFP reporter cell line to examine replication capacity of CXCR4- and CCR5-tropic HIV-1 by flow cytometry.

The rate of HIV-1 disease progression correlates strongly with plasma viral load and is likely to be influenced by both host and viral determinants. Though interest in the impact of viral replication capacity during HIV-1 infection has been increasing, especially with respect to drug resistance mutations, its influence on disease course remains poorly understood. This is due in part to significant drawbacks in conventional means of measuring HIV-1 growth in vitro (i.e. expense, inconvenience, and experimental variability). A FACS-based method is described here to measure HIV-1 replication sensitively and a modification of this method can be used to determine viral titer accurately. Importantly, the target cells used are permissive to CXCR4- and CCR5-tropic HIV-1 strains. In pilot experiments, the growth kinetics of laboratory-adapted strains NL4-3 and IIIB were examined carefully. Using this method, differences were observed in growth kinetics between three laboratory strains and seven primary isolates, indicating the potential for a broad range of in vitro replication capacities among individual isolates. In conclusion, this FACS-based method provides a sensitive approach to measure the replication capacity of HIV-1 and may prove useful in studies examining the impact of viral fitness on disease progression.

Cell Line↗

PubMed2005

Broad repertoire of the CD4+ Th cell response in spontaneously controlled hepatitis C virus infection includes dominant and highly promiscuous epitopes.

A vigorous hepatitis C virus (HCV)-specific Th cell response is regarded as essential to the immunological control of HCV viremia. The aim of this study was to comprehensively define the breadth and specificity of dominant HCV-specific CD4(+) T cell epitopes in large cohorts of subjects with chronic and spontaneously resolved HCV viremia. Following in vitro stimulation of PBMC, HCV-specific cell cultures from each subject were screened with an overlapping panel of synthetic 20-mer peptides spanning the entire HCV polyprotein. Of 22 subjects who spontaneously controlled HCV viremia, all recognized at least one of a group of six epitopes situated within the nonstructural (NS) proteins NS3, NS4, and NS5, each of which was detected by >30% of subjects, but most subjects recognized additional, more heterogeneous specificities. In contrast, none of the most frequently targeted epitopes was detected by >5% of persons with chronic infection. The most frequently recognized peptides showed promiscuous binding to multiple HLA-DR molecules in in vitro binding assays and were restricted by different HLA-DR molecules in functional assays in different persons. These data demonstrate that predominant CD4(+) T cell epitopes in persons with resolved HCV infection are preferentially located in the nonstructural proteins and are immunogenic in the context of multiple class II molecules. This comprehensive characterization of CD4(+) T cell epitopes in resolved HCV infection provides important information to facilitate studies of immunopathogenesis and HCV vaccine design and evaluation.

Cells, Cultured↗

PubMed2005

A microchip CD4 counting method for HIV monitoring in resource-poor settings.

BACKGROUND: More than 35 million people in developing countries are living with HIV infection. An enormous global effort is now underway to bring antiretroviral treatment to at least 3 million of those infected. While drug prices have dropped considerably, the cost and technical complexity of laboratory tests essential for the management of HIV disease, such as CD4 cell counts, remain prohibitive. New, simple, and affordable methods for measuring CD4 cells that can be implemented in resource-scarce settings are urgently needed. METHODS AND FINDINGS: Here we describe the development of a prototype for a simple, rapid, and affordable method for counting CD4 lymphocytes. Microliter volumes of blood without further sample preparation are stained with fluorescent antibodies, captured on a membrane within a miniaturized flow cell and imaged through microscope optics with the type of charge-coupled device developed for digital camera technology. An associated computer algorithm converts the raw digital image into absolute CD4 counts and CD4 percentages in real time. The accuracy of this prototype system was validated through testing in the United States and Botswana, and showed close agreement with standard flow cytometry (r = 0.95) over a range of absolute CD4 counts, and the ability to discriminate clinically relevant CD4 count thresholds with high sensitivity and specificity. CONCLUSION: Advances in the adaptation of new technologies to biomedical detection systems, such as the one described here, promise to make complex diagnostics for HIV and other infectious diseases a practical global reality.

Algorithms↗

PubMed2005

Impact of Kaposi sarcoma-associated herpesvirus (KSHV) burden and HIV coinfection on the detection of T cell responses to KSHV ORF73 and ORF65 proteins.

Cellular immune responses to Kaposi sarcoma-associated herpesvirus (KSHV), the etiological agent of KS and several other malignancies, are incompletely characterized. We assessed KSHV-specific interferon- gamma enzyme-linked immunospot responses in a cohort of 154 individuals, using overlapping peptide sets spanning the KSHV-encoded latency-associated nuclear antigen (ORF73) and the minor capsid glycoprotein (ORF65). Among KSHV-seropositive subjects, ORF73-specific responses dominated over responses to ORF65 and were preferentially detected in human immunodeficiency virus-coinfected individuals who had elevated levels of cell-associated KSHV DNA, indicating that the viral antigen burden may have been driving these responses. Responses to both ORF73 and ORF65 were also detected in several KSHV-seronegative subjects who were at increased risk for KSHV infection, which demonstrates that cellular immunity can be found in the absence of detectable humoral responses. These data have implications for the reliable identification of KSHV infection and may help guide the design of immune-based therapeutic and prophylactic interventions.

Antigens, Viral↗