High burden of clonal hematopoiesis in first responders exposed to the World Trade Center disaster.

The terrorist attacks on the World Trade Center (WTC) created an unprecedented environmental exposure to aerosolized dust, gases and potential carcinogens. Clonal hematopoiesis (CH) is defined as the acquisition of somatic mutations in blood cells and is associated with smoking and exposure to genotoxic stimuli. Here we show that deep targeted sequencing of blood samples identified a significantly higher proportion of WTC-exposed first responders with CH (10%; 48 out of 481) when compared with non-WTC-exposed firefighters (6.7%; 17 out of 255; odds ratio, 3.14; 95% confidence interval, 1.64-6.03; P = 0.0006) after controlling for age, sex and race/ethnicity. The frequency of somatic mutations in WTC-exposed first responders showed an age-related increase and predominantly affected DNMT3A, TET2 and other CH-associated genes. Exposure of lymphoblastoid cells to WTC particulate matter led to dysregulation of DNA replication at common fragile sites in vitro. Moreover, mice treated with WTC particulate matter developed an increased burden of mutations in hematopoietic stem and progenitor cell compartments. In summary, the high burden of CH in WTC-exposed first responders provides a rationale for enhanced screening and preventative efforts in this population.

Leukemic Transdifferentiation of Follicular Lymphoma Into an Acute Histiocytic Leukemia in a 52-Year-Old Caucasian Woman.

We report an instructive case of acute myeloid leukemia with histiocytic differentiation (acute histiocytic leukemia) arising in a patient, a 52-year-old woman with a history of follicular lymphoma. The results of genetic studies proved a clonal relationship between the lymphoma and the leukemic cells. To our knowledge, this is the first report of leukemic transdifferentiation of follicular lymphoma into modified base 5-methylcytosine (M(5)c)-like acute histiocytic leukemia and the first reported karyotype on a transdifferentiated neoplasm.

A single S1034C mutation confers altered drug sensitivity to PfMDR1 ATPase activity that is characteristic of the 7G8 isoform.

The mechanism behind how PfMDR1 may contribute to antimalarial drug resistance is unclear. Transfection studies suggest that PfMDR1 mutations may make small contributions to drug sensitivity in a strain-dependent fashion, whereas field data link over expression (not necessarily mutation) of the gene with clinical drug treatment failure. This study dissects the contribution of individual mutations of PfMDR1 that contribute to the unique behavior of the 7G8 PfMDR1 isoform. A single mutation in putative TM 11 (S1034C) is found to abolish drug stimulation of PfMDR1 ATPase activity.

Heterologous expression and ATPase activity of mutant versus wild type PfMDR1 protein.

Mutation of the P. falciparum chloroquine resistance transporter (PfCRT) causes resistance to chloroquine (CQ) and other antimalarial drugs. Mutation and/or overexpression of one of the multidrug resistance protein homologues found in this malarial parasite (PfMDR1) may further modify or tailor the degree of multidrug resistance. However, considerable controversy surrounds the precise contribution of PfMDR1, in part because no direct biochemical studies of PfMDR1 have yet been possible. Using codon optimization and other principles, we have designed and constructed a yeast optimized version of the wild type pfmdr1 gene and have successfully overexpressed PfMDR1 protein in P. pastoris yeast. The protein is well expressed in either full length form or as two separate half transporters, is well localized to the yeast plasma membrane and is fully functional as evidenced by ATPase activity measurements. We have also expressed mutants that have previously been hypothesized to influence drug resistance in parasites. Using purified plasma membrane fractions, we have analyzed antimalarial drug effects on ATPase activity for wild type versus mutant proteins. Relative to other ABCB transporters involved in drug resistance, PfMDR1 is unusual. It has similar pH, [ATP], and Mg++ dependencies for ATP hydrolysis, yet relatively high Km and Vmax values for ATP hydrolysis, and ATPase activity is only mildly stimulated by antimalarial drugs. The largest measured drug effect is for CQ (to which PfMDR1 is not believed to confer resistance), and it is strongly inhibitory for WT PfMDR1. Drug resistance associated PfMDR1 mutants show either elevated (Dd2 allele encoded) or reduced (7G8 allele) basal ATPase activity and different patterns of drug stimulation or inhibition, relative to WT PfMDR1. The Dd2 PfMDR1 isoform also shows a slightly more alkaline pH optimum. Surprisingly, verapamil alone (1-300 microM) does not significantly affect WT ATPase activity but inhibits the Dd2 isoform at 1 microM. These data should assist ongoing analysis of the contribution of PfMDR1 to antimalarial drug resistance.