Early, Persistent Lymphopenia Is Associated With Prolonged Multiple Organ Failure and Mortality in Septic Children.

OBJECTIVES: Sepsis-associated immune suppression correlates with poor outcomes. Adult trials are evaluating immune support therapies. Limited data exist to support consideration of immunomodulation in pediatric sepsis. We tested the hypothesis that early, persistent lymphopenia predicts worse outcomes in pediatric severe sepsis. DESIGN: Observational cohort comparing children with severe sepsis and early, persistent lymphopenia (absolute lymphocyte count < 1,000 cells/µL on 2 d between study days 0-5) to children without. The composite outcome was prolonged multiple organ dysfunction syndrome (MODS, organ dysfunction beyond day 7) or PICU mortality. SETTING: Nine PICUs in the National Institutes of Health Collaborative Pediatric Critical Care Research Network between 2015 and 2017. PATIENTS: Children with severe sepsis and indwelling arterial and/or central venous catheters. INTERVENTIONS: Blood sampling and clinical data analysis. MEASUREMENTS AND MAIN RESULTS: Among 401 pediatric patients with severe sepsis, 152 (38%) had persistent lymphopenia. These patients were older, had higher illness severity, and were more likely to have underlying comorbidities including solid organ transplant or malignancy. Persistent lymphopenia was associated with the composite outcome prolonged MODS or PICU mortality (66/152, 43% vs 45/249, 18%; p < 0.01) and its components prolonged MODS (59/152 [39%] vs 43/249 [17%]), and PICU mortality (32/152, 21% vs 12/249, 5%; p < 0.01) versus children without. After adjusting for baseline factors at enrollment, the presence of persistent lymphopenia was associated with an odds ratio of 2.98 (95% CI [1.85-4.02]; p < 0.01) for the composite outcome. Lymphocyte count trajectories showed that patients with persistent lymphopenia generally did not recover lymphocyte counts during the study, had lower nadir whole blood tumor necrosis factor-α response to lipopolysaccharide stimulation, and higher maximal inflammatory markers (C-reactive protein and ferritin) during days 0-3 ( p < 0.01). CONCLUSIONS: Children with severe sepsis and persistent lymphopenia are at risk of prolonged MODS or PICU mortality. This evidence supports testing therapies for pediatric severe sepsis patients risk-stratified by early, persistent lymphopenia.

Rationale for Adjunctive Therapies for Pediatric Sepsis Induced Multiple Organ Failure.

Adjunctive therapies have been proposed for use in at least 5 inflammation pathobiology phenotypes in pediatric sepsis-induced multiple organ failure. This article discusses host-pathogen interaction prototypes to facilitate understanding of the rationale for personalized therapy in these phenotypes. The article discusses the literature on adjunctive antiinflammatory and immune modulation therapies that, in addition to traditional organ support and infection source control, might be part of a personalized precision medicine approach to the reversal of each of these inflammatory pathobiology phenotypes.

Late postnatal expansion of self-reactive CD8alphaalpha+ intestinal intraepithelial lymphocytes in mice.

The intestinal epithelium is unique in that it harbors auto-reactive T cells largely absent from the peripheral TCR repertoire in normal mice. Intestinal intraepithelial lymphocytes (IEL) expressing self-reactive TCR are mostly CD8alphaalpha+ cells in adult H-Y TCR RAG(-/-) male mice homozygous for the restricting MHC I allele, H-2D(b). By contrast, in male mice heterozygous for the restricting and non-restricting MHC I allele, H-2D(d) (MHC F(1), H-2D(b/d)), IEL are composed of CD8alphabeta and CD8alphaalpha+ T cells. Here we demonstrate that IEL in the immediate postnatal period of MHC homozygous male mice were mostly CD8(-) T cells, while IEL in MHC F(1) male mice were CD8(-) and CD8alphabeta+ T cells. Regardless of the MHC I configuration and the ability to support positive selection of CD8alphabeta+ cells in the thymus, the expansion of CD8alphaalpha+ IEL was a late postnatal event that followed a reduction in CD8(-) IEL. Furthermore, although in vivo treatment with the specific peptide antigen resulted in an earlier accumulation of activated IEL, the expansion of CD8alphaalpha+ IEL remained inefficient until late in postnatal life. Finally, as CD8(-) IEL stimulated with TCR agonists in vitro, acquired expression of CD8alphaalpha, we propose that CD8alphaalpha+ IEL derive from CD8(-) IEL intermediates. Whether CD8(-) IEL are CD8alphabeta-lineage cells that escape deletion in the thymus or are T cells targeted to the intestine from the thymus because of the early and high level TCR transgene expression in this model, is not clear. The signals required for the expansion of CD8alphaalpha+ IEL are however, incomplete in the immediate postnatal intestine. Determining the factors required for the expansion or retention of CD8alphaalpha+ IEL bearing high affinity, self-specific TCR will further elucidate the in vivo role of these T cells in intestinal homeostasis and perhaps, autoimmunity.

T cells in cryptopatch aggregates share TCR gamma variable region junctional sequences with gamma delta T cells in the small intestinal epithelium of mice.

The role of cryptopatch aggregates in the development of intestinal intraepithelial lymphocytes (IEL) is a matter of controversy. Therefore, an important question is whether T cells in cryptopatch aggregates are lineally related to IEL. We hypothesized that if gammadelta+ IEL derive from T cells in cryptopatch aggregates, then a clonal relationship would exist between the two populations. To test this hypothesis, we compared the sequence of rearranged TCR gamma variable region 5 genes in gammadelta+ IEL and cryptopatch cells. We purified IEL by FACS and cryptopatch cells were isolated from frozen sections of the intestine by laser-assisted microdissection. PCR showed that TCR gamma variable region 5 was rearranged in gammadelta+ IEL and in CD3+ cryptopatch cells, but not in CD3- cryptopatch cells. DNA sequence analysis showed that the frequency of in-frame junctions in cryptopatch aggregates was at a level consistent with positive selection in both wild-type and athymic nude mice. In addition, the predicted amino acid sequences of V-J junctions present in gammadelta+ IEL and cryptopatch cells were encoded by identical nucleotide sequences. By contrast, the frequency of in-frame joints was significantly reduced in cryptopatch cells isolated from TCR delta-deficient mice, indicating that the enrichment of in-frame joints in cryptopatch cells must normally depend on expression of surface gammadelta TCR. Our results are consistent with the hypothesis that a subset of gammadelta+ IEL are related to T cells in cryptopatch aggregates. The precise role of cryptopatch aggregates in intestinal gammadelta+ T cell homeostasis still needs to be determined.