ABSTRACT: Various inborn errors of the canonical NF-kB pathway underlie different forms of human immunodeficiency. However, no patients with autosomal recessive complete deficiencies of RelA, c-REL, or NF-kB1, the three core members of the canonical NF-kB pathway, have yet been identified. We report a child homozygous for a loss-of-expression mutation of REL, encoding c-REL, which is expressed principally in myeloid and lymphoid cells. The distribution of myeloid subsets is normal in this patient, but in vitro-derived monocytes and cDC1s, unlike cDC2s, have impaired IL-12 and IL-23 production. The patient has low frequencies of memory CD4+ T cells, Th1*, Th2, Tregs, and almost no memory B cells. The frequencies of the other lymphoid subsets are normal. The patient’s naïve and memory CD4+ T cells produce only small amounts of IL-2, and the addition of this interleukin rescues their proliferation in response to mitogens, but not to antigens, in vitro. However, we found that HLA-syngeneic control cDCs rescued the proliferation of these cells in response to recall antigens. The production of key effector cytokines, such as IL-4, IL-17A, and IFNg, by memory CD4+ T cells was also highly impaired ex vivo, as was the differentiation of naïve CD4+ T cells into Th1 and Th17 cells in vitro. Both the survival and proliferation of the patient’s naïve B cells were found to be compromised, preventing B-cell differentiation into immunoglobulin (Ig)-secreting plasmablasts in vitro. As a consequence of this pleiotropic effect, this child suffered from severe viral, mycobacterial, fungal, and parasitic infections, while IgG substitution treatment prevented pyogenic infections. The immunological and infectious phenotypes were of hematopoietic origin, as they were cured by hematopoietic stem cell transplantation. Inherited human c-REL deficiency impairs multiple core functions of DCs, T cells, and B cells, thereby disrupting adaptive immunity to multiple infections.
