Common cytokine receptor gamma chain (gammac)-deficient B cells persist in T cell-deficient gammac-mice and respond to a T-independent antigen.

Defects in the common cytokine receptor gamma chain (gammac) in man result in X-linked severe combined immunodeficiency disease (SCIDX1) characterized by an absence of alphabeta T cells, gammadelta T cells and NK cells, with the presence of circulating B cells. Mice made deficient for gammac lack gammadelta T cells and NK cells, but in contrast to SCIDX1 patients have appreciable numbers of alphabeta T cells, while B cells are reduced about tenfold in numbers and disappear with age. Here we show that when gammac- mice are rendered T cell deficient, B cell numbers are still reduced but the age-dependent loss of B cells does not occur. The peripheral B cells which persisted in gammac-/ nude and gammac-/TCRbeta-/- mice were able to respond to mitogen stimulation in vitro and to mount antigen-specific T-independent Ig responses in vivo. These results demonstrate that gammac- B cells are functionally competent and suggest that residual alphabeta T cells are implicated in the B cell loss in gammac mice. The gammac-/nude and gammac-/TCRbeta-/- mice provide new models to dissect the role of gammac-dependent receptors during murine B cell differentiation.

Stable and functional lymphoid reconstitution of common cytokine receptor gamma chain deficient mice by retroviral-mediated gene transfer.

Mutations in the gene encoding the common cytokine receptor gamma chain (gamma(c)) are responsible for human X-linked severe combined immunodeficiency disease (SCIDX1). We have used a gamma(c)-deficient mouse model to test the feasibility and potential toxicity of gamma(c) gene transfer as a therapy for SCIDX1. A retrovirus harboring the murine gamma(c) chain was introduced into gamma(c)-deficient bone marrow cells, which were then transplanted into alymphoid RAG2/gamma(c) double-deficient recipient mice. Circulating lymphocytes appeared 4 weeks postgraft and achieved steady-state levels by 8 weeks. The mature lymphocytes present in the grafted mice had integrated the gamma(c) transgene, expressed gamma(c) transcripts, and were able to proliferate in response to gamma(c)-dependent cytokines. The gamma(c)-transduced animals demonstrated (1) normal levels of immunoglobulin subclasses, including immunoglobulin G1 (IgG1) and IgG2a (which are severely decreased in gamma(c)(-) mice); (2) the ability to mount an antigen-specific, T-dependent antibody response showing effective in vivo T-B cell cooperation, and (3) the presence of gut-associated cryptopatches and intraepithelial lymphocytes. Importantly, peripheral B and T cells were still present 47 weeks after a primary graft, and animals receiving a secondary graft of gamma(c)-transduced bone marrow cells demonstrated peripheral lymphoid reconstitution. That gamma(c) gene transfer to hematopoietic precursor cells can correct the immune system abnormalities in gamma(c)(-) mice supports the feasibility of in vivo retroviral gene transfer as a treatment for human SCIDX1.

Deregulated TCR alpha beta T cell population provokes extramedullary hematopoiesis in mice deficient in the common gamma chain.

Deficiency of the cytokine receptor common gamma chain (gamma c) results in abnormal lymphoid development and a severe immunodeficiency disease due to the combined loss of the receptors for interleukins (IL)-2, -4, -7, -9, and -15. We have observed the development of secondary hematopoiesis with circulating hematopoietic progenitor cells in adult mice harboring a null mutation in gamma c. These extramedullary changes were not secondary to bone marrow failure or to an inability to maintain circulating blood counts. These results suggested that gamma c-dependent cytokine signaling pathways modulate hematopoietic development. An intrinsic defect in gamma c- hematopoietic stem cell commitment appeared unlikely, as fetal liver hematopoiesis was unaltered in gamma c- embryos. Furthermore, the absence of natural killer cells in gamma c- mice was not responsible for the observed hematopoietic changes. Peripheral TCR alpha beta T cells from gamma c- mice were characterized by an activated phenotype (CD62Llo, CD44hi, CD69hi) and showed increased levels of transcripts for hematopoietic stimulating cytokines, including IL-3 and granulocyte/macrophage-colony-stimulating factor. A predominance of these cells was detected in the bone marrow, suggesting a role for residual T cells in the enhanced hematopoiesis. Strikingly, the elimination of residual T cells from gamma c- mice reduced splenic and circulating hematopoietic precursor frequencies to normal levels. These results clearly implicate a deregulated TCR alpha beta T cell population in the observed hematopoietic changes in gamma c- mice, and emphasize the importance of gamma c-dependent cytokine interactions in modulating mature T cell responses.

Lineage relationships and differentiation of natural killer (NK) T cells: intrathymic selection and interleukin (IL)-4 production in the absence of NKR-P1 and Ly49 molecules.

In this report, we have assessed the lineage relationships and cytokine dependency of natural killer (NK) T cells compared with mainstream TCR-alphabeta T cells and NK cells. For this purpose, we studied common gamma chain (gamma c)-deficient mice, which demonstrate a selective defect in CD3- NK cell development relative to conventional TCR-alphabeta T cells. NK thymocytes differentiate in gamma c- mice as shown by the normal percentage of TCR Vbeta8+ CD4-CD8- cells and the normal quantity of thymic Va14-Jalpha281 mRNA that characterize the NK T repertoire. However, gamma c-deficient NK thymocytes fail to coexpress the NK-associated markers NKR-P1 or Ly49, yet retain characteristic expression of the cytokine receptors interleukin (IL)-7R alpha and IL-2Rbeta. Despite these phenotypic abnormalities, gamma c- NK thymocytes could produce normal amounts of IL-4. These results define a maturational progression of NK thymocyte differentiation where intrathymic selection and IL-4-producing capacity can be clearly dissociated from the acquisition of the NK phenotype. Moreover, these data suggest a closer ontogenic relationship of NK T cells to TCR-alphabeta T cells than to NK cells with respect to cytokine dependency. We also failed to detect peripheral NK T cells in these mice, demonstrating that gamma c-dependent interactions are required for export and/or survival of NK T cells from the thymus. These results suggest a stepwise pattern of differentiation for thymically derived NK T cells: primary selection via their invariant TCR to confer the IL-4-producing phenotype, followed by acquisition of NK-associated markers and maturation/export to the periphery.