Langerhans cell histiocytosis (LCH) is now understood to be a neoplastic disease in which over 50% of cases have somatic activating mutations of BRAF. However, the extracellular signal-related (ERK) pathway is activated in all cases including those with wild type BRAF alleles. Here, we applied a targeted massively parallel sequencing panel to 30 LCH samples to test for the presence of additional genetic alterations that might cause ERK pathway activation. In 20 BRAF wild type samples, we found 3 somatic mutations in MAP2K1 (MEK1) including C121S and C121S/G128D in the kinase domain, and 56_61QKQKVG>R, an in-frame deletion in the N-terminal regulatory domain. All three variant proteins constitutively phosphorylated ERK in in vitro kinase assays. The C121S/G128D and 56_61QKQKVG>R variants were resistant to the mitogen-activated protein kinase kinase (MEK) inhibitor trametinib in vitro. Within the entire sample set, we found 3 specimens with mutations in MAP3K1 (MEKK1), including two truncation mutants, T779fs and T1481fs; T1481fs encoded an unstable and nonfunctional protein when expressed in vitro. T779fs was present in a specimen carrying BRAF V600E. The third variant was a single nucleotide substitution, E1286V, which was fully functional and is likely a germline polymorphism. These results indicate that LCH cells can harbor additional genetic alterations in the RAS-RAF-MEK pathway which, in the case of MAP2K1, may be responsible for ERK activation in a wild type BRAF setting. The resistance of some of these variants to trametinib may also have clinical implications for the combined use of RAF and MEK inhibitors in LCH.

Although an increasing proportion of elderly patients with colon cancer are treated with adjuvant chemotherapy, many elderly patients still do not receive this treatment. As expected, receipt of adjuvant treatment decreased in the presence of comorbidity, but the clinical rationale for undertreatment of women and patients with low socioeconomic status is not clear.

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SLC27a2) 40-fold and increased FA transport 4-fold compared to resting (naïve) T cells (see Table). Donor T cells also increased levels of enzymes necessary for FA oxidation (e.g. CPT2) 100-fold and oxidized more FAs. Mitochondrial mass (required for FA oxidation) increased in donor T cells, as did the ratio of mitochondrial to nuclear DNA, and the expression of PGC-1a, a key regulator of mitochondrial biogenesis. Importantly, T cells proliferating during routine immune reconstitution (following syngeneic BMT) minimally increased FA transport (10% vs. 40% in GVHD T cells). Finally, inhibition of FA oxidation in vivo, through irreversible blockade of CPT1 with etomoxir, decreased the total number of well-divided donor T cells after a single dose. Furthermore, two weeks of etomoxir treatment, beginning on day +7, improved both GVHD clinical score (1.1 vs. 3.8 in untreated animals, P ¼ .02) and weight loss at day 40. In total, these data demonstrate that GVHD T cells up-regulate FA metabolism in vivo and that proliferating, donor cells can be selectively eliminated through inhibition of FA oxidation. Our data provide novel insights into the metabolism of lymphocytes activated in vivo and show that inhibition of FA oxidation may be a therapeutic target for the prevention and/ or treatment of GVHD.