HLA-C and HIV-1: a matter of stability

HLA-C requires β2-microglobulin (β2m) for proper folding and cell surface expression. The HLA-C gene is highly polymorphic, encoding different allotypes classified in stable and unstable clusters, based on their binding stability to β2m. Unstable HLA-C molecules release more β2m than stable variants, generating more HLA-C free chains on the cell surface. HLA-C plays an important role in modulating HIV -1 infection. It has been reported that a higher HLA-C expression is associated with better HIV-1 infection control, while its lower expression leads to a rapid progression toward AIDS. Highly and lowly expressed HLA-C alleles have been defined as protective and non-protective, respectively, in relation to HIV-1 disease progression. Differently, in our previous studies, we reported that HIV-1 virions lacking HLA-C have reduced infectivity and increased susceptibility to neutralizing antibodies. The reasons behind this apparent contradiction were explained by our recent findings showing that HIV-1 Env interacts with HLA-C freechains, after their dissociation from β2m, and that protective HLA-C alleles bind β2m more efficiently (“stable” variants), compared to non-protective alleles presenting more free chains on the cell surface (“unstable” variants). It is known that patients affected by AIDS Dementia Complex (ADC), a very severe neurological condition of HIV-1 infection, present high level of β2m in the cerebrospinal fluid. We propose that the outcome of HIV-1 infection might be driven both by HLA-C surface expression levels and by HLA-C/β2m binding stability. According to this model, the expression of unstable variants leads to a higher β2m shedding and to a reduction of immunocompetent HLA-C complexes expressed on the cell surface. Consequently, the increase of HLA-C free chains raises viral infectivity contributing to a rapid progression toward AIDS. This model was supported by our recent findings showing that unstable HLA-C variants are more frequently associated with the development of ADC in HIV-1 infected patients. To further investigate the contribution of HLA-C variants in HIV-1 infection, we used CRISPR/Cas9 to develop an HLA-C KO human cell line. The different HLA-C alleles have been then restored by transfection, generating cell lines expressing each a specific HLA-C allotype. To assign a binding stability score to each HLA-C variant, an acid wash treatment will be performed to study the kinetic of β2m detachment. Furthermore, to evaluate the HIV-1 infectivity modulation, each HLA-C expressing cell line will be employed to produce HIV-1 pseudotyped viruses to be tested in infectivity assays. This study will allow us to stratify HLA-C alleles according to their binding stability to β2m and to clarify the relationship between HLA-C allotypes binding stability, HIV-1 infection progression and HIV-1 related neurocognitive disorders onset