Platelet-medicated deregulation of dendritic cell function- implications for anti-HIV immune responses and immunotherapy

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ABSTRACT We will test the hypothesis that the disruption of platelet-monocyte and platelet-DC complexes will result in improved function of DCs, thereby increasing the efficacy of a) spontaneous control of HIV and b) the therapeutic effects of DC based immunotherapy. We have reported that HIV infection results in up to 2-fold increase in circulating platelet-monocyte complexes (PMCs) resulting in undesirable activation of monocytes. Our latest in vitro preliminary data show that DCs derived from PMCs (MoDCs) express reduced levels of several molecules critical to DC function (e.g. CD206, DC-SIGN, CD80, CD86, CCR7) and show reduced antigen uptake capacity, ability to induce the proliferation of naïve CD4 and CD8 T cells and decreased IL-12 secretion upon stimulation with CD40L. Increased levels of TGF in co-culture supernatants are suggestive that this molecule may mediate the suppressive effects of platelets on MoDCs. We also detected direct complexes between platelets and circulating DCs (cDCs) in whole blood of HIV+ and HIV- individuals, that were associated with decreased expression of CD40 and CD80 suggesting that, similar to other leukocytes, platelets can influence endogenous DC function.Guided by these observations, in Aim 1 we will determine the effect of platelets on the immunogenic functions of endogenous blood-isolated cDC1, cDC2, pDC and MoDC. To this end, HIV infected, cART treated and uninfected individuals on or not on anti-platelet therapy will be enrolled using our active protocols. Circulating DCs will be analyzed for their interaction with platelets and expression of costimulatory molecules and chemokine receptors. These findings will be correlated with measures of platelet activation and HIV specific immune responses by ELISPOT. Further, cDCs (directly isolated from blood) or MoDCs will be complexed with platelets to evaluate their production of immunostimultory and suppressive factors, and used to evaluate antigen presentation to naïve CD4 and CD8 T cells, migration towards lymph-node-directing chemokines (CCL21, CCL19), in vitro induction of Th1 and CTL responses against HIV and control antigens and cytotoxic function. Aim 2, will determine the role of TGF and PGE2 signaling in platelet-mediated modulation of MoDC and cDC function. Blocking antibodies/inhibitors of TGF and PGE2 will be used. Identification of the key signaliing events associated with DC-modulating effects of platelets will allow us to develop new strategies to improve inherent anti-HIV immune responses in infected individuals, and, potentially other chronic disorders including cancer.