Self-reactive and transplacental-acquired maternal T cells in SCID patients—time to update

Abstract

Patients with severe combined immunodeficiency (SCID) typically present with profoundly reduced T cells. In some cases, however, T cells may be affected by defects that allow some T-cell development but compromise T-cell function such as in Omenn syndrome (OS), which is characterized by impaired T cell differentiation in the presence of abnormal self-reactive cells. One distinctive feature of SCID patients, which can sometimes resemble the clinical picture of OS, is the presence of alloreactive cells that originated from transplacentally acquired maternal T lymphocytes. The traditional view is that self-reactive cells and transplacentally acquired maternal T cells cannot occur concomitantly in the same OS patient. This review provides an updated functional characterization of transplacentally acquired maternal T cells and compares them with the T cells of an OS patient. An unusual case of an immunodeficient SCID patient with a mild OS phenotype is also presented. This patient had both self-reactive cells and transplacentally acquired maternal T cells, allowing us to simultaneously evaluate the function and tolerance capacities of both cell types. We propose that coexistence of autologous and maternal T cells in patients exhibiting mild OS symptoms was rejected because it had not been studied before and not because the cells are mutually exclusive. Moreover, taking into consideration the milder clinical phenotype associated with transplacentally acquired maternal T cells in SCID patients, we believe that these cells may provide some degree of immunity and prevent autoimmunity, even though they do not actually function to protect against infections.Statement of novelty: Autologous and transplacental-acquired maternal T cells can coexist in the same SCID patient. Although both cell types are nonfunctional for protecting against infections, maternal cells provide some degree of immunity and therefore are associated with only mild GVHD symptoms.