PD-1, a T cell checkpoint receptor and target of cancer immunotherapy, is also expressed on myeloid cells. The role of myeloid-specific versus T cell–specific PD-1 ablation on antitumor immunity has remained unclear because most studies have used either PD-1–blocking antibodies or complete PD-1 KO mice. We generated a conditional allele, which allowed myeloid-specific (PD-1f/fLysMcre) or T cell–specific (PD-1f/fCD4cre) targeting of Pdcd1 gene. Compared with T cell–specific PD-1 ablation, myeloid cell–specific PD-1 ablation more effectively decreased tumor growth. We found that granulocyte/macrophage progenitors (GMPs), which accumulate during cancer-driven emergency myelopoiesis and give rise to myeloid-derived suppressor cells (MDSCs), express PD-1. In tumor-bearing PD-1f/fLysMcre but not PD-1f/fCD4cre mice, accumulation of GMP and MDSC was prevented, whereas systemic output of effector myeloid cells was increased. Myeloid cell–specific PD-1 ablation induced an increase of T effector memory cells with improved functionality and mediated antitumor protection despite preserved PD-1 expression in T cells. In PD-1–deficient myeloid progenitors, growth factors driving emergency myelopoiesis induced increased metabolic intermediates of glycolysis, pentose phosphate pathway, and TCA cycle but, most prominently, elevated cholesterol. Because cholesterol is required for differentiation of inflammatory macrophages and DC and promotes antigen-presenting function, our findings indicate that metabolic reprogramming of emergency myelopoiesis and differentiation of effector myeloid cells might be a key mechanism of antitumor immunity mediated by PD-1 blockade.

PDZK1, a multi-PDZ domain containing adaptor protein, interacts with various membrane proteins, including the high density lipoprotein (HDL) receptor scavenger receptor class B type I (SR-BI). Here we show that PDZK1 controls in a tissue-specific and post-transcriptional fashion the expression of SR-BI in vivo. SR-BI protein expression in PDZK1 knock-out (KO) mice was reduced by 95% in the liver, 50% in the proximal intestine, and not affected in steroidogenic organs (adrenal, ovary, and testis). Thus, PDZK1 joins a growing list of adaptors that control tissue-specific activity of cell surface receptors. Hepatic expression of SR-BII, a minor splice variant with an alternative C-terminal cytoplasmic domain, was not affected in PDZK1 KO mice, suggesting that binding of PDZK1 to SR-BI is required for controlling hepatic SR-BI expression. The loss of hepatic SR-BI was the likely cause of the elevation in plasma total and HDL cholesterol and the increase in HDL particle size in PDZK1 KO mice, phenotypes similar to those observed in SR-BI KO mice. PDZK1 KO mice differed from SR-BI KO mice in that the ratio of unesterified to total plasma cholesterol was normal, females were fertile, and cholesteryl ester stores in steroidogenic organs were essentially unaffected. These differences may be due to nearly normal extrahepatic expression of SR-BI in PDZK1 KO mice. The PDZK1-dependent regulation of hepatic SR-BI and, thus, lipoprotein metabolism supports the proposal that this adaptor may represent a new target for therapeutic intervention in cardiovascular disease.

The organization of lin genes and IS6100 was studied in three strains of Sphingomonas paucimobilis (B90A, Sp؉, and UT26) which degraded hexachlorocyclohexane (HCH) isomers but which had been isolated at different geographical locations. DNA-DNA hybridization data revealed that most of the lin genes in these strains were associated with IS6100, an insertion sequence classified in the IS6 family and initially found in Mycobacterium fortuitum. Eleven, six, and five copies of IS6100 were detected in B90A, Sp؉, and UT26, respectively. IS6100 elements in B90A were sequenced from five, one, and one regions of the genomes of B90A, Sp؉, and UT26, respectively, and were found to be identical. DNA-DNA hybridization and DNA sequencing of cosmid clones also revealed that S. paucimobilis B90A contains three and two copies of linX and linA, respectively, compared to only one copy of these genes in strains Sp؉ and UT26. Although the copy number and the sequence of the remaining genes of the HCH degradative pathway (linB, linC, linD, and linE) were nearly the same in all strains, there were striking differences in the organization of the linA genes as a result of replacement of portions of DNA sequences by IS6100, which gave them a strange mosaic configuration. Spontaneous deletion of linD and linE from B90A and of linA from Sp؉ occurred and was associated either with deletion of a copy of IS6100 or changes in IS6100 profiles. The evidence gathered in this study, coupled with the observation that the G؉C contents of the linA genes are lower than that of the remaining DNA sequence of S. paucimobilis, strongly suggests that all these strains acquired the linA gene through horizontal gene transfer mediated by IS6100. The association of IS6100 with the rest of the lin genes further suggests that IS6100 played a role in shaping the current lin gene organization.Hexachlorocyclohexane (HCH) was introduced for the control of agricultural pests and of vector-borne diseases in early 1940s. While this compound was used extensively all over the world, several reports on the persistence of HCH isomers (␣, ␤, ␥, and ␦) and their toxic effects on nontarget organisms appeared in the 1980s (11). These reports finally resulted in a ban on or restricted use of HCH in most countries. Neither the ban nor the restricted use has, however, reduced the levels of HCH residues in the environment (6, 25, 33), especially in soils that had a previous history of HCH application (2). One serious problem is the uptake of HCH residues from soil by crops, which then enter food products (1, 31). In addition to no further use of HCH, a decontamination program for HCHpolluted soils would diminish the risk posed by HCH residues to human, plant, and animal health. One possibility for decontamination is spontaneous or induced microbial degradation. Unfortunately, spontaneous microbial degradation of HCH isomers proceeds rather slowly (10, 15), although a number of bacteria which can degrade one or more isomers of HCH have been isolated. Thus, addition of naturally occu...