Studio della risposta immunitaria umorale anti-Tat in soggetti HIV-1 positivi

The Tat regulatory protein of human immunodeficiency virus type 1 (HIV-1) plays a key role in viral infectivity and HIV-1 infection progression to AIDS. In natural infection, Tat represents an important target for the host immune response: it is able to stimulate both a cell-mediated immune response (Th1) capable of controlling virus replication in the acute phase of infection and a humoral immune response (Th2) with the presence of circulating antibodies that correlates with a slower infection progression. This is an important aspect in order to the development of a therapeutic vaccination strategy able to counteract Tat protein activities and, therefore, the HIV-1 virus spread. The aim of this work was to analyze the anti-Tat antibody response in the natural HIV-1 infection with relation to the immunological status (CD4+ T cell count), levels of viral replication (HIV RNA copies/ml) and persistence of virus (cellular HIV DNA copies/104 CD4). Regarding the HIV-1 genetic variability, we studied the antibody response against the Tat protein of HIV-1 clade B, which is the predominant strain in Europe, and clade C, in particular against two Tat variants that differ for the cysteine content: Cys30Ser31 and Cys30Cys31 Tat clade C. Subtype C is largely predominant in Asia and Southern and Eastern Africa, where there is the largest outbreak of HIV-1 infection worldwide. First of all, we took care to develop and optimize three ELISA assays to detect specific IgG against the three Tat antigens. In the optimization phase, we defined the reference values of standards (positive control, negative control and background) in order to ensure the functionality and reproducibility of tests, and the cut-off value, for each Tat antigens, required to discriminate HIV-1 infected individuals with circulating anti-Tat antibodies from non-presenting patients. 6 Subsequently, we analyzed anti B-Tat IgG response in a cohort of European HIV-1 positive subjects and evaluated the presence and cross-clade reactivity of immunoglobulins type G against three Tat antigens in a cohort of African patients. Our data suggest a positive clinical status when the anti-Tat antibody response is present with respect to its absence. Nevertheless, the presence of anti-Tat antibodies does not seem to be a prerogative of a positive clinical condition: in a situation of high viral activity, an intensive stimulation of immune response may occur that may be responsible of an anti-Tat polyclonal antibody response that seems to be characterized by non-protective immunoglobulins. Moreover, concerning the genetic heterogeneity of circulating HIV-1 subtypes, our results seem to suggest that variations in Tat protein may be responsible of differences in its processing as antigen with effects on the release of protective antibodies and with “cross-clade reactivity” properties. In particular, immunoglobulins able to recognize clade B Tat protein seem to be involved in protective effects of the anti-Tat antibody response as opposed to antibodies reactive against clade C Tat variants. Furthermore, it would seem to be present a “clade-specificity” concerning the stimulation of a cross-clade reactive and protective anti-Tat antibody response linked to infection caused by CRF 02_AG and, especially, by subtype B. Further studies are needed to better understand the features of the regulatory protein and of the anti-Tat immune response, not neglecting differences between several circulating viral subtypes and recombinant forms, considering the Tat protein use as vaccine antigen for HIV/AIDS vaccine development.