*Purpose: Undernutrition has been associated with T cell immune cell dysfunction and infectious complications in non-immunosuppressed children. Thus, we aimed to define T cell phenotypes associated with undernutrition that may predispose children to viral events post-transplantation.

*Methods: 104 children (age 1-21) from the multi-center, NIH, Immune Development in Pediatric Transplantation (IMPACT) trial were prospectively monitored for 1 year after kidney transplantation. Undernutrition was defined as z-score less than 2 SD for weight, height, and body mass index. Patients were categorized as having no event, impaired protective immunity defined by PCR positive viremia/clinical viral infection, or alloimmune failure characterized by donor specific antibody development or biopsy proven acute rejection. Multiparameter flow cytometry was monitored for naïve CD45RA+CCR7+, central memory CD45RA-CCR7+, effector memory CD45RA-CCR7-, effector memory RA CD45RA+CCR7-, senescent (CD57+), and exhausted (PD1+) CD4/CD8 T cells.

*Results: Of 104 children, 98 had nutritional data available. Undernourished patients were disproportionately represented (36.4%) in the 64 patients with impaired protective immunity compared to the 15 patients with no event (18.8%) or the 19 patients with alloimmune failure (27.3%). Undernourished recipients had higher naïve CD4, lower effector memory CD4 and lower CD8 effector memory T cells (Fig 1a-c) pre-transplantation (baseline) compared to their nourished counterparts. This T cell phenotype persisted in undernourished patients across all 3 clinical outcome groups (Figure 2 a-c).

*Conclusions: Undernutrition is associated with posttransplant viremia and evidence of impaired peripheral T cell maturation. This should be taken into consideration when tailoring immunotherapy and optimizing nutrition.

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