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We previously reported the clinical phenotype of two siblings with a novel inherited developmental and immunodeficiency syndrome consisting of severe intrauterine growth retardation and the impaired development of specific lymphoid lineages, including transient CD8 alphabeta T lymphopenia and a persistent lack of blood NK cells. We describe here the elucidation of a plausible underlying pathogenic mechanism, with a cellular phenotype of impaired survival of both fresh and herpesvirus saimiri-transformed T cells, in the surviving child. Clearly, NK cells could not be studied. However, peripheral blood T lymphocytes displayed excessive apoptosis ex vivo. Moreover, the survival rates of CD4 and CD8 alphabeta T cell blasts generated in vitro, and herpesvirus saimiri-transformed T cells cultured in vitro, were low, but not nil, following treatment with IL-2 and IL-15. In contrast, Fas-mediated activation-induced cell death was not enhanced, indicating a selective excess of cytokine deprivation-mediated apoptosis. In keeping with the known roles of IL-2 and IL-15 in the development of NK and CD8 T cells in the mouse model, these data suggest that an impaired, but not abolished, survival response to IL-2 and IL-15 accounts for the persistent lack of NK cells and the transient CD8 alphabeta T lymphopenia documented in vivo. Impaired cytokine-mediated lymphocyte survival is likely to be the pathogenic mechanism underlying this novel form of inherited and selective NK deficiency in humans.

We have shown that in vitro infection herpesvirus saimiri (HVS) can transform human CD4+ T cell clones with defined Th1 or Th2 cytokine profiles to continuous growth. We report here that transformation with HVS enabled both Th1 and Th2 clones to stimulate proliferation and Ig production by autologous or allogeneic B cells in the absence of stimulants. The polyclonal B cell-activating property of HVS-transformed clones was not related to free virus or soluble cytokines, but rather was dependent on an Ag-nonspecific, MHC-unrestricted, contact-dependent mechanism. T blasts from unstimulated HVS-transformed clones did not express CD40 ligand (CD40L) mRNA or CD40L protein, whereas a proportion of them constitutively expressed membrane TNF (mTNF)-alpha. Both CD40L and mTNF-alpha were detectable on either uninfected or HVS-transformed clones upon mitogen stimulation. The activation of high-density B cells by unstimulated HVS-transformed clones was not inhibited by soluble CD40-Ig fusion protein, but was strongly reduced by either anti-TNF-alpha or anti-TNF-alpha receptor (TNF-alpha R) mAbs. Addition of anti-CD2 and/or anti-CD58 mAbs was also inhibitory, but no additive effect with anti-TNF-alpha and/or anti-TNF-alpha R mAbs was observed. Neither anti-IL-2 nor CD40-Ig inhibited the proliferation of naive IgD+ B cells cocultured with fixed unstimulated HVS-transformed clones, whereas a combination of anti-TNF-alpha and anti-TNF-alpha R mAbs was inhibitory. In addition, fixed unstimulated HVS-transformed clones induced Ig synthesis in IgD+ naive B cells even in the absence of exogenous IL-2. Data suggest that both the mTNF-alpha/TNF-alpha R and the CD2/CD58 pathways, but not the CD40L-CD40 interaction plus secreted cytokines, are involved in the unusual mode of B cell activation exerted by CD4+ HVS-transformed clones.

T blasts of six established human CD4+ T cell clones with defined Ag specificity and cytokine secretion profile (3 Th1 and 3 Th2) were immortalized with Herpesvirus saimiri (HVS) and compared with their uninfected counterparts for their ability to proliferate, produce cytokines, and express cytolytic activity. HVS-transformed Th1 and Th2 clones neither substantially changed their original surface markers nor lose their ability to proliferate in response to their specific Ag but did acquire the ability to proliferate in response to contact signals delivered by SRBC or autologous APC alone. In addition, transformation by HVS substantially enhanced the lectin-dependent cytolytic activity of Th1 clones and enabled noncytolytic Th2 clones to exert cytolytic activity. HVS-transformed Th1 clones but not their uninfected counterparts spontaneously transcribed and secreted Th1-type cytokines (IL-2, IFN-gamma, and TNF-beta) and such a production was further enhanced by stimulation with either SRBC or PMA plus anti-CD3 mAb. HVS transformed but not uninfected Th2 clones constitutively expressed both IL-4 and IL-2 mRNA and secreted IFN-gamma. Stimulation with PMA plus anti-CD3 mAb induced uninfected Th2 clones to secrete high amounts of IL-4 and IL-5 but not Th1-type cytokines, whereas the same HVS-transformed Th2 showed minimal IL-4 and IL-5 secretion with concomitant high production of IL-2, IFN-gamma, and TNF-beta. Transformation by HVS also resulted in up-regulation of TNF-alpha and IL-3 production by both Th1 and Th2 clones. The ongoing proliferation of HVS-transformed clones was partially inhibited by either anti-IL-2 or anti-IL-3 antibodies and virtually abolished by the combined addition of the two anticytokine antibodies, suggesting that both IL-2 and IL-3 can function as autocrine growth factors for HVS-transformed Th1 and Th2 clones.