Tshaka Cunningham

Cellular inhibitors with Fv1-like activity restrict human and simian immunodeficiency virus tropism

Many nonhuman primate cells are unable to support the replication of HIV-1, whereas others are nonpermissive for infection by simian immunodeficiency virus from macaques (SIVmac). Here, we show that restricted HIV-1 and SIVmac infection of primate cell lines shares some salient features with Fv1 and Ref1-mediated restriction of murine retrovirus infection. In particular, the nonpermissive phenotype is most evident at low multiplicities of infection, results in reduced accumulation of reverse transcription products, and is dominant in heterokaryons generated by fusion of permissive and nonpermissive target cells. Moreover, in nonpermissive primate cells, HIV-1 and SIVmac infection is cooperative, and enveloped HIV-1 virus-like particles, minimally containing Gag and protease, abrogate restriction. In African green monkey cells, HIV-1 virus-like particles ablate restrictions to HIV-1 and SIVmac, suggesting that both are restricted by the same factor. Finally, a virus that contains an HIV-1 capsid-p2 domain in an SIVmac background exhibits a tropism for primate cells that is HIV-1-like rather than SIVmac-like. These data indicate the existence of one or more saturable inhibitors that are polymorphic in primates and prevent HIV and SIV infection by targeting the capsid of the incoming lentivirus particle.

MHC class I antigen processing distinguishes endogenous antigens based on their translation from cellular vs. viral mRNA

To better understand the generation of MHC class I-associated peptides, we used a model antigenic protein whose proteasome-mediated degradation is rapidly and reversibly controlled by Shield-1, a cell-permeant drug. When expressed from a stably transfected gene, the efficiency of antigen presentation is ∼2%, that is, one cell-surface MHC class I–peptide complex is generated for every 50 folded source proteins degraded upon Shield-1 withdrawal. By contrast, when the same protein is expressed by vaccinia virus, its antigen presentation efficiency is reduced ∼10-fold to values similar to those reported for other vaccinia virus-encoded model antigens. Virus infection per se does not modify the efficiency of antigen processing. Rather, the efficiency difference between cellular and virus-encoded antigens is based on whether the antigen is synthesized from transgene- vs. virus-encoded mRNA. Thus, class I antigen-processing machinery can distinguish folded proteins based on the precise details of their synthesis to modulate antigen presentation efficiency.

Graduate Journal: Wrapping things up

After emerging from my penultimate thesis committee meeting, I experienced a range of bittersweet emotions underscored by a profound sense of nostalgia. Although I am thrilled about finishing my PhD and moving on to a postdoc at the Pasteur Institute in Paris, I will be sad to leave New York and Rockefeller University.