2) Escape of HIV-1 from HIV-1-specific CTLs
We found that novel escape mutants were selected by CTLs having strong ability to suppress HIV-1 replication. We investigated the accumulation of escape mutations at 9 cohorts in the world with Dr. Philip Goulder's group in Oxford University (ref 4). We analyzed viral sequences and HLA alleles from > 2,800 subjects, drawn from 9 distinct study cohorts spanning 5 continents. Initial analysis of the HLA-B*51-restricted epitope, TAFTIPSI (RT 128-135), showed a strong correlation between the frequency of the escape mutation, I135X, and HLA-B*51 prevalence in the 9 study cohorts (p=0.0001). Extending these analyses to incorporate other well-defined CD8⁺ T-cell epitopes, including those restricted by HLA-B*57 and B*27, showed that the frequency of these epitope variants (n=14) was consistently correlated with the prevalence of the restricting HLA allele in the 9 cohorts (together, p < 0.0001), demonstrating strong evidence of HIV adaptation to HLA at a population level. This process of viral adaptation may dismantle the well-established HLA associations with control of HIV infection that are linked to the availability of key epitopes, and highlights the challenge for a vaccine to keep pace with the changing immunological landscape presented by HIV. We are now analyzing other HLA class I-restricted CTL responses and HIV-1 mutations in Japanese donors who were recently infected with HIV-1.
It still remains unclear if escape mutant-specific CTLs are definitively not elicited in new hosts sharing donor HLA molecules. Nef138-10-2F is known as escape mutant from Nef138-10-specific CTLs We found the existence of the Nef138-10-2F-specific CTLs in 3 new hosts who had been primarily infected with the 2F mutant. The 2F-specific CTL clones suppressed the replication of both wild-type and mutant viruses. However, the ability of these clones to suppress the replication of the 2F virus was much weaker than that of wild-type-specific and the 2F-specific ones to suppress the replication of the wild-type virus. These findings indicate that the 2F mutant is conserved in the HIV-1-infected donors having HLA-A*2402, because the 2F-specific CTLs failed to suppress completely the 2F mutant replication and effectively prevented viral reversion in new hosts carrying HLA-A*2402 (ref 5).

3) Mechanism of HIV-1-specific CD4 T cells to recognize HIV-1
It is well known that A HIV-1-specific CD4 T cells have crucial role in suppression of HIV-1 replication. Most of these T cells play a role as helper T cells. A restricted number of studies have shown that HIV-1-specific cytotoxic CD4⁺ T cells are present in HIV-1-infected individuals. We investigated the role of HIV-1-specific CD4 CTLs. We identified novel DRB1*0803⁺-restricted Nef epitope-specific cytotoxic CD4⁺ T cells. The Nef-specific CD4⁺ T cell clones exhibited strong cytotoxic activity against both HIV-1-infected macrophages and CD4⁺ T cells. In addition, these Nef-specific cytotoxic CD4⁺ T cells exhibited strong ability to suppress HIV-1 replication in both macrophages and in CD4⁺ T cells in vitro. These Nef-specific cytotoxic CD4⁺ T cells were detected in 40% of DRB1*0803⁺donors. Thus our study suggested that these HIV-1-specific cytotoxic CD4⁺ T cells may contribute to control of HIV-1 in vivo by suppressing virus replication in HIV-1 natural host cells (ref. 6).

2. AIDS vaccine development

To develop mice model for AIDS vaccine development, we generated humanized mice by transplanting CD34⁺ human cells into NOD/Scid/Jak3 deficient (NOJ) newborn mice. Established mice had human immune cells such as T cells (both CD4 and CD8 T cells), B cells, and macrophages. However the CD8 T cells showed immature characteristics (CD27CD28CD45RA markers and expression of perforin and granzame A/B), suggesting that this humanized mice have no or weak T cell responses to antigens. We are now making NOJ mice expressing HLA-B*5101(NOJ-B*5101). NOJ-B*5101 will be expected to have mature T cells because positive and negative selection of CD8 ⁺ T cells work in thymus of the mice. In addition, we are developing AIDS therapeutic vaccine for Japanese population with Oxford University group (Drs. Andrew MacMichael and Thomas Hanke).