Use of interleukin-7, interleukin-2, and interferon-γ to propagate CD4₊T cells in culture with maintained antigen specificity

In contrast to CD8₊T cells, it has been difficult to establish consistently satisfactory conditions for the bulk culture of antitumor CD4₊T cells in either mice or humans. This difficulty is not limited to tumor antigen, since similar problems are encountered growing CD4₊T cells that recognize alloantigen, tetanus, or candida. Four basic findings are reviewed in this article, stemming from work with identical results in both human and mouse. (a) Although CD4₊T cells initially proliferate after exposure to appropriate antigen-presenting cells (APCs), such proliferation is not sustained; however, expansion of CD4₊T cells can be achieved with the addition of recombinant interleukin-2 (rIL2) or rIL-7. (b) Specific CD4₊responses to antigens are often better sustained with exogenous IL-7 than with exogenous IL-2. (c) Adding rIL-7 or rIL-2 permits sustained CD4₊T-cell proliferation, but subsequent culture restimulation is complicated by high background reactivity to APCs whether APCs are antigen pulsed or not; this problem can be overcome by addition of exogenous interferon-γ (IFN-γ) to the CD4₊cultures. (d) In certain instances proliferation is paradoxically impaired by reexposure to specific antigen, possibly reflecting apoptosis; this problem is also overcome by addition of rINF-γ to culture. We conclude that combinations of exogenous IL-7, IL-2, and IFN-γ with APC restimulation can be used to sustain antigen-specific CD4₊T cells in culture. Using these techniques, antitumor CD4₊T cells were propagated from the peripheral blood of two tumor-bearing patients.