Cooperativity between T cell receptor complexes revealed by conformational mutants of CD3epsilon.

The CD3epsilon subunit of the T cell receptor (TCR) complex undergoes a conformational change upon ligand binding that is thought to be important for the activation of T cells. To study this process, we built a molecular dynamics model of the transmission of the conformational change within the ectodomains of CD3. The model showed that the CD3 dimers underwent a stiffening effect that was funneled to the base of the CD3epsilon subunit. Mutation of two relevant amino acid residues blocked transmission of the conformational change and the differentiation and activation of T cells. Furthermore, this inhibition occurred even in the presence of excess endogenous CD3epsilon subunits. These results emphasize the importance of the conformational change in CD3epsilon for the activation of T cells and suggest the existence of unforeseen cooperativity between TCR complexes.

Expression of a modified form of CD4 results in the release of an anti-HIV factor derived from the Env sequence.

We have studied the inhibitory effect of a CD4 chimera (CD4epsilon15) on HIV replication. This chimera is retained in the endoplasmic reticulum and traps the HIV envelope precursor gp160, preventing its maturation. Retroviral expression of the chimera strongly inhibited HIV replication even when it is expressed by only a minority of the T cell population. This protective effect on bystander nontransduced cells is mediated by a soluble factor that we identified as a fragment of HIV gp120 envelope protein and accordingly, we named this factor Env-derived antiviral factor (EDAF). Biochemical and immunoreactivity data show that EDAF is comprised of the gp120 C3-C5 regions and indeed, a recombinant protein bearing this sequence reproduces the anti-HIV properties of EDAF. Surprisingly, three tryptic peptides derived from EDAF are homologous but not identical with the corresponding sequences of the HIV isolate used to generate EDAF. We propose that EDAF results from an alternative intracellular processing of the Env protein provoked by its association to CD4epsilon15 and the selection of the best fitted Env protein sequences contained within the HIV isolate. The presence of EDAF improves the therapeutic potential of the CD4epsilon15 gene and it opens new possibilities for antiviral treatment and vaccine development.

Human TCR that incorporate CD3zeta induce highly preferred pairing between TCRalpha and beta chains following gene transfer.

TCR gene therapy is adversely affected by newly formed TCRalphabeta heterodimers comprising exogenous and endogenous TCR chains that dilute expression of transgenic TCRalphabeta dimers and are potentially self-reactive. We have addressed TCR mispairing by using a modified two-chain TCR that encompasses total human CD3zeta with specificities for three different Ags. Transfer of either TCRalpha:CD3zeta or beta:CD3zeta genes alone does not result in surface expression, whereas transfer of both modified TCR chains results in high surface expression, binding of peptide-MHC complexes and Ag-specific T cell functions. Genetic introduction of TCRalphabeta:zeta does not compromise surface expression and functions of an endogenous TCRalphabeta. Flow cytometry fluorescence resonance energy transfer and biochemical analyses demonstrate that TCRalphabeta:CD3zeta is the first strategy that results in highly preferred pairing between CD3zeta-modified TCRalpha and beta chains as well as absence of TCR mispairing between TCR:CD3zeta and nonmodified TCR chains. Intracellular assembly and surface expression of TCR:CD3zeta chains is independent of endogenous CD3gamma, delta, and epsilon. Taken together, our data support the use of TCRalphabeta:CD3zeta to prevent TCR mispairing, which may provide an adequate strategy to enhance efficacy and safety of TCR gene transfer.