Epidermodysplasia Verruciformis and Vδ2 γδ T-cell Expansion in STK4 Deficiency.

The clinical penetrance of infectious diseases varies considerably among patients with inborn errors of immunity (IEI), even for identical genetic defects. This variability is influenced by pathogen exposure, healthcare access and host-environment interactions. We describe here a patient in his thirties who presented with epidermodysplasia verruciformis (EV) due to infection with a weakly virulent beta-papillomavirus (HPV38) and CD4⁺ T-cell lymphopenia. The patient was born to consanguineous parents living in the United States. Exome sequencing identified a previously unknown biallelic STK4 stop-gain mutation (p.Trp425X). The patient had no relevant history of infectious disease during childhood other than mild wart-like lesion on the skin, but he developed diffuse large B-cell lymphoma (DLBCL) and EBV viremia with a low viral load in his thirties. Despite his low CD4⁺ T-cell count, the patient had normal counts of CD3⁺ cells, predominantly double-negative T cells (67.4%), which turned out to be Vδ2⁺ γδ T cells. γδ T-cell expansion has frequently been observed in the 33 reported cases with STK4 deficiency. The Vδ2 γδ T cells of this STK4-deficient patient are mostly CD45RA^-CD27⁺CCR7⁺ central memory γδT cells, and their ability to proliferate in response to T-cell activation was impaired, as was that of CD4⁺ T cells. In conclusion, γδ T-cell expansion may act as a compensatory mechanism to combat viral infection, providing immune protection in immunocompromised individuals.