Comprehensive Analysis Of Human Immunodeficiency Virus Type 1-Specific Immunodominant Cytotoxic T-Lymphocyte Responses And CD4~+T Helper Cell Responses In China

Acquired immunodeficiency syndrome (AIDS) is a worldwide infectious disease, which is mainly caused by Human Immunodeficiency Virus type I (HIV-1).It's estimated that the pepple living with HIV worldwide are 33.2 million and about 2.5 million people were newly infected with HIV in 2007. Every day, over 6800 persons become infected with HIV and over 5700 persons die of AIDS, mostly because of inadequate access to HIV prevention and treatment services. Efforts to control disease progression associated with HIV-1 infection have led to the use of a combination of antiviral drugs, referred to highly active antiretroviral therapy (HAART). Despite the initial success of HAART in controlling HIV-1 replication and dramatically decreasing morbidity and mortality of AIDS, there are many limitations of this treatment, including serious side effects of the drugs, emergence of drug-resistant, HIV-1 mutants and poor adherence. Thus the need for a vaccine that protects against HIV-1 infection or attenuates disease has never been more urgent. Logically speaking, understanding the correlates of protective immunity is the first step in vaccine development. In the case of HIV-1 immunity, accumulative data have proved the central role of HIV-1-specific CTL and T helper cells in controlling viral replication. However, the generation of strong HIV-specific CTLs in infected individuals fails to control the infection completely in the majority of patients because of the absence of CD4+T helper cells. Therefore CD4+T helper cells become necessary for effective neutralizing antibody mediating virus clearance. Comprehensive analysis of HIV-1-specific immunodominant CTL responses and CD4+T cell responses is essential for the design of HIV-1 vaccine. Moreover the identification of HIV-1-specific CTL and CD4+T helper cells optimal epitopes is the important step in the development of candidate vaccine. The specificity of HIV-1-reactive cellular immune responses depends largely on the genetic background of population, as CTL epitopes are presented to the T cell receptor by HLA class I molecule on their peptides biding cleft of cell surfaces. Therefore, it is vital to study virus-specific CTL responses in different HIV-1 epidemic regions and ethnic groups. Both the common alleles of Chinese population and the mainly circulating viral strain are different from those in other regions, so the profile of Th responses and CTL responses may be different from that in Caucasian and Africa populations. However, very little is known about the characterization of HIV-1-specific immunodominant CTL responses and CD4+T helper cell responses in Chinese HIV-1 infected individuals. So it is very significant to develop a safe, effective and feasible HIV-1vaccine for China.HIV-1 Clade B (HIV-1B) is the main circulating strain in China. In our study, we performed HLA typing, plasma viral load quantitation, and comprehensive mapping of CTL responses against the peptides restricted by individual subject's HLA-alleles to describe the individual epitopes targeted during chronic HIV-1 infection and their immunodominance pattern, and to assess the relative contribution of CTL responses against the peptides scanning optimal epitopes restricted by each HLA allele to the total HIV-1-specific response detected in each subject expressing respective allele and their correlations with viral load and CD4+ T cell count. Meanwhile we characterized HIV-1-specific CD4+T cell responses in 14 HIV-1-infected individuals during chronic HIV-1 infection, using a set of 94 overlapping peptides spanning HIV-1 B Gag and Nef proteins, and identified immunodominant regions of these proteins. The major findings and results of our study are as follows:HLA class I alleles were tested by Polymerase chain reaction with sequence -specific primers(PCR-SSP) in a cohort of 102 HIV-1 infected individuals and ten alleles were expressed in over 20% of our study population:A*02, A*24, A*11, B*13,B*46,B*15,Cw*03,Cw*01,Cw*07 and Cw*06, which is consistent with the previous findings. The frequency of two HLA class I alleles B*27 and B*57 was less than 3%, which had been strongly associated with long-term non-progressive chronic HIV-1 infection in Caucasian. These findings indicated that the genetic background of our cohort well matched that of the Chinese population.HIV-1-specific CTL responses against a panel of 413 overlapping peptides spanning HIV-1 Clade B sequence, including 165 peptides corresponding to described optimal clade B epitopes, in 102 HIV-1 infected individuals were analyzed by gamma interferon enzyme-linked immunospot (ELISpot) assay to assess the immunodominance patterns of CTL responses.1. We analyzed the difference of the percentage between chronic infected individuals and AIDS patients. The average percentages of subjects with detectable responses restricted by HLA- A*2, -A*24, -B*07, -B*15 and -B*58 in chronic infected individuals were higher than those in AIDS patients (P=0.017, P=0.041, P=0.004, P=0.005 and P=0.042; respectively), while for HLA-A*11 the opposite result was found between these two groups (P=0.020). No significant associations(r=0.014,P=0.923) between the contribution of HIV-1- specific immunodominant CTL responses restricted by every subject's four HLA alleles(HLA-A and -B) to the total virus-specific immune response and viral loads were discovered in the individuals in chronic infected individuals. There was a significant negative correlation (r=-0.321,P=0.026) between that contribution and viral loads in AIDS patients, regardless of their treatment. These data showed that the ability of these responses against the peptides restricted by their respective HLA class I alleles might play an important protective role at terminal stage of HIV-1 infection.2. Using 94 overlapping peptides spanning HIV-1Gag and Nef proteins (based on the clade B consensus sequence), fresh CD4+ T cells from 14 subjects during chronic HIV-1 infection were screened for the breadth and specificity of HIV-1-specific CD4+ T cell responses by ELISpot assay. Regardless of the treatment and the disease progression, HIV-1-specific CD4+ T cell responses were detectable in Gag p17, p24, p15 and Nef proteins. Neither the total magnitude nor the breadth of responses correlated with viral loads (P>0.05). Seventeen immunodominant regions were defined by the frequency >20% and normalized cumulative Th cell responses >50 SFC/106Th cells. In a subgroup of nine individuals, HIV-1-specific Th cell responses of seven individuals can be more broadly detected than CTL responses can in the same person.In summary, the correlation between HLA class I alleles and disease progression was observed in the study on the immunodominance patterns of HIV-1-specific CTL responses in 102 HIV-1 infected individuals. Our research indicated that the ability of the responses against the immunodominance peptides restricted by their respective HLA class I alleles might play an important protective role at terminal stage of HIV-1 infection. There was a significantly different profile of HIV-1-specific CD4+ T cell responses between Chinese and Caucasians. Seventeen immunodominant regions of CD4+ T cell responses were identified in this study. HIV-1-specific Th cell responses of seven individuals can be more broadly detected than CTL responses can in the same person. These observations provide the rationale for further investigation of immunotherapeutic approaches and shed light on relevant immune responses that may be crucial for vaccine development.