Targeting intracellular oncoproteins with dimeric IgA promotes expulsion from the cytoplasm and immune-mediated control of epithelial cancers

Dimeric IgA (dIgA) can move through cells via the IgA/IgM polymeric immunoglobulin receptor (PIGR), which is expressed mainly on mucosal epithelia. Here, we studied the ability of dIgA to target commonly mutated cytoplasmic oncodrivers. Mutation-specific dIgA, but not IgG, neutralized KRASG12D within ovarian carcinoma cells and expelled this oncodriver from tumor cells. dIgA binding changed endosomal trafficking of KRASG12D from accumulation in recycling endosomes to aggregation in the early/late endosomes through which dIgA transcytoses. dIgA targeting of KRASG12D abrogated tumor cell proliferation in cell culture assays. In vivo, KRASG12D-specific dIgA1 limited the growth of KRASG12D-mutated ovarian and lung carcinomas in a manner dependent on CD8+ T cells. dIgA specific for IDH1R132H reduced colon cancer growth, demonstrating effective targeting of a cytoplasmic oncodriver not associated with surface receptors. dIgA targeting of KRASG12D restricted tumor growth more effectively than small-molecule KRASG12D inhibitors, supporting the potential of this approach for the treatment of human cancers.

Sézary syndrome originates from heavily mutated hematopoietic progenitors

The pathogenesis of cutaneous T-cell lymphoma (CTCL) remains unclear. Using single-cell RNA or T-cell receptor (TCR) sequencing of 32 619 CD3+CD4+ and CD26+/CD7+ and 29 932 CD3+CD4+ and CD26-/CD7- lymphocytes from the peripheral blood of 7 patients with CTCL, coupled to single-cell ATAC-sequencing of 26,411 CD3+CD4+ and CD26+/CD7+ and 33 841 CD3+CD4+ and CD26-/CD7- lymphocytes, we show that tumor cells in Sézary syndrome and mycosis fungoides (MF) exhibit different phenotypes and trajectories of differentiation. When compared to MF, Sézary cells exhibit narrower repertoires of TCRs and exhibit clonal enrichment. Surprisingly, we identified ≥200 mutations in hematopoietic stem cells from multiple patients with Sézary syndrome. Mutations in key oncogenes were also present in peripheral Sézary cells, which also showed the hallmarks of recent thymic egression. Together our data suggest that CTCL arises from mutated lymphocyte progenitors that acquire TCRs in the thymus, which complete their malignant transformation in the periphery.

Actionable spontaneous antibody responses antagonize malignant progression in ovarian carcinoma

OBJECTIVE

To demonstrate that shared antibody responses in endometriosis and endometriosis-associated ovarian cancer spontaneously antagonize malignant progression and can be leveraged to develop future immunotherapies.

METHODS

B cells from cyopreserved clear cell ovarian carcinoma (CCC, n = 2), endometrioid ovarian carcinoma (EC, n = 2), and endometriomas (n = 2) were isolated, activated, and EBV-immortalized. Antibodies were purified from B cell supernatants and used for screening arrays containing most of the human proteome. Targets were prioritized based on accessibility (transmembrane or secreted proteins), expression in endometriosis and cancer, and concurrent IgA and IgG responses. We focused on antibodies targeting tumor-promoting syndecan binding protein (SDCBP) to demonstrate anti-tumor activity. Immunoblots and qPCR were performed to assess SDCBP expression in ovarian cancer and endometriosis cell lines and tumor samples. Recombinant IgG4 was generated using the variable heavy and light chains of dominant B cell receptors (BCRs) reacting against the extracellular domain of SDCBP, and used in in vivo studies in human CCC- and high-grade serous ovarian carcinoma (HGSOC)-bearing immunodeficient mice.

RESULTS

Nine accessible proteins detected by both IgA and IgG were identified in all samples - including SDCBP, which is expressed in ovarian carcinomas of multiple histologies. Administration of α-SDCBP IgG4 in OVCAR3 (HGSOC), TOV21G and RMG-I (CCC) tumor-bearing mice significantly decreased tumor volume compared to control irrelevant IgG4.

CONCLUSIONS

Spontaneous antibody responses exert suboptimal but measurable immune pressure against malignant progression in ovarian carcinomas. Using tumor-derived antibodies for developing novel immunotherapeutics warrants further investigation.

Olfactory Receptor OR2H1 Is an Effective Target for CAR T Cells in Human Epithelial Tumors

Although chimeric antigen receptor (CAR)-expressing T cells have proven success in hematologic malignancies, their effectiveness in solid tumors has been largely unsuccessful thus far. We found that some olfactory receptors are expressed in a variety of solid tumors of different histologic subtypes, with a limited pattern of expression in normal tissues. Quantification of OR2H1 expression by qRT-PCR and Western blot analysis of 17 normal tissues, 82 ovarian cancers of various histologies, eight non-small cell lung cancers (NSCLCs), and 17 breast cancers demonstrated widespread OR2H1 expression in solid epithelial tumors with expression in normal human tissues limited to the testis. CAR T cells recognizing the extracellular domain of the olfactory receptor OR2H1 were generated with a targeting motif identified through the screening of a phage display library and demonstrated OR2H1-specific cytotoxic killing in vitro and in vivo, using tumor cells with spontaneous expression of variable OR2H1 levels. Importantly, recombinant OR2H1 IgG generated with the VH/VL sequences of the CAR construct specifically detected OR2H1 protein signal in 60 human lung cancers, 40 ovarian carcinomas, and 73 cholangiocarcinomas, at positivity rates comparable with mRNA expression and without OR2H1 staining in 58 normal tissues. CRISPR/Cas9-mediated ablation of OR2H1 confirmed targeting specificity of the CAR and the tumor-promoting role of OR2H1 in glucose metabolism. Therefore, T cells redirected against OR2H1-expressing tumor cells represent a promising therapy against a broad range of epithelial cancers, likely with an admissible toxicity profile.

Utilization of immortalized B cells to identify SDCBP as a novel therapeutic target in ovarian carcinoma

e14507

Background: We hypothesized that tumor-infiltrating B cells in endometriosis and endometriosis-associated ovarian cancer can be used to identify novel, targetable antigen domains to inhibit the progression of ovarian carcinomas. We aimed to identify targets that are spontaneously recognized by B-cell-derived antibodies within ovarian clear cell carcinoma (CCC), endometrioid carcinoma (EC), and endometriosis and to determine the preclinical anti-cancer efficacy of a candidate antibody that recognizes the extracellular domain of an identified target. Methods: B cells from freshly dissociated CCC (n = 2), EC (n = 2), and endometriomas (n = 2) were isolated, activated, and EBV-immortalized. Antibodies were purified from B cell supernatants and used for screening in a proteome array. Targets were prioritized based on accessibility (transmembrane or secreted proteins), expression in endometriosis and cancer, and concurrent IgA and IgG responses. Tumor-promoting syndecan binding protein (SDCBP) was identified and SDCBP-reactive B cells were FACS-sorted and subjected to single cell B cell receptor sequencing to determine the variable heavy and light chain sequences of enriched clonotypes. We then generated a recombinant IgG4 antibody targeting SDCBP with the dominant VH/VL matching sequences. Immunoblots and qPCR were performed to assess SDCBP expression in ovarian cancer cell lines and tumor samples. In vivo studies compared anti-tumor potential of the α-SDCBP IgG4 with controls using immunodeficient mouse models of human CCC and high-grade serous ovarian carcinoma (HGSOC). Results: Nine accessible proteins were detected by both IgA and IgG in all samples, including SDCBP. SDCBP is expressed in ovarian cancer cell lines and tumor samples of multiple histologies, including CCC, EC, and HGSOC. Administration of α-SDCBP IgG4 in TOV21G (CCC) tumor-bearing mice significantly decreased tumor volume compared to non-antigen-specific irrelevant IgG4 (iIgG4, p = 0.002) and vehicle (0.001), and correspondingly trended toward decreased tumor weight compared to vehicle (p = 0.06). Likewise, administration of α-SDCBP IgG4 in OVCAR3 (HGSOC) tumor-bearing mice significantly decreased tumor volume compared to iIgG4 (p = 0.03) and trended toward decreased tumor weight (p = 0.06). Conclusions: An α-SDCBP IgG4 has demonstrated anti-tumor efficacy in SDCBP+ CCC and HGSOC, and SDCBP-targeted therapy for endometriosis and associated malignant conditions, as well as HGSOC, warrants further investigation.

Ovarian cancer immunogenicity is governed by a narrow subset of progenitor tissue-resident memory T cells

Despite repeated associations between T cell infiltration and outcome, human ovarian cancer remains poorly responsive to immunotherapy. We report that the hallmarks of tumor recognition in ovarian cancer-infiltrating T cells are primarily restricted to tissue-resident memory (TRM) cells. Single-cell RNA/TCR/ATAC sequencing of 83,454 CD3+CD8+CD103+CD69+ TRM cells and immunohistochemistry of 122 high-grade serous ovarian cancers shows that only progenitor (TCF1low) tissue-resident T cells (TRMstem cells), but not recirculating TCF1+ T cells, predict ovarian cancer outcome. TRMstem cells arise from transitional recirculating T cells, which depends on antigen affinity/persistence, resulting in oligoclonal, trogocytic, effector lymphocytes that eventually become exhausted. Therefore, ovarian cancer is indeed an immunogenic disease, but that depends on ∼13% of CD8+ tumor-infiltrating T cells (∼3% of CD8+ clonotypes), which are primed against high-affinity antigens and maintain waves of effector TRM-like cells. Our results define the signature of relevant tumor-reactive T cells in human ovarian cancer, which could be applicable to other tumors with unideal mutational burden.

Spontaneous class-switched antibody responses at endometrial cancer tumor bed drives superior patients’ outcome

The role of humoral responses in endometrial cancer remains insufficiently investigated. Using a cohort of 107 patients with different histological subtypes of endometrial carcinoma, we report that concomitant accumulation of T, B and plasma cells at tumor beds predicts better survival. However, only B cell markers predict survival specifically in high-grade endometrioid type and serous tumors. Accordingly, immune protection is associated with class-switched IgA and, to a lesser extent, IgG. Notably, expression of polymeric immunoglobulin receptor (pIgR) by tumor cells and its occupancy by IgA are superior predictors of outcome, and correlate with defects in methyl mismatch repair. Mechanistically, pIgR-dependent, antigen-independent IgA occupancy drives inflammatory pathways associated with IFN and TNF signaling in tumor cells, along with apoptotic and ER stress pathways, while thwarting DNA repair mechanisms. Therefore, coordinated humoral and cellular immune responses, characterized by IgA:pIgR interactions in tumor cells, determine the progression of human endometrial cancer, and therefore the potential for effective immunotherapies.

Supported by grants from NIH (R01CA157664, R01CA124515, R01CA178687 and R01CA211913), and from Cancer Center Support Grant (CCSG) CA076292

TGF-β-mediated silencing of genomic organizer SATB1 promotes Tfh cell differentiation and formation of intra-tumoral tertiary lymphoid structures

The immune checkpoint receptor PD-1 on T follicular helper (Tfh) cells promotes Tfh:B cell interactions and appropriate positioning within tissues. Here, we examined the impact of regulation of PD-1 expression by the genomic organizer SATB1 on Tfh cell differentiation. Vaccination of CD4^CreSatb1^f/f mice enriched for antigen-specific Tfh cells, and TGF-β-mediated repression of SATB1 enhanced Tfh differentiation of human T cells. Mechanistically, high Icos expression in Satb1^-/- CD4⁺ T cells promoted Tfh cell differentiation by preventing T follicular regulatory cell skewing and resulted in increased isotype-switched B cell responses in vivo. Ovarian tumors in CD4^CreSatb1^f/f mice accumulated tumor antigen-specific, LIGHT⁺CXCL13⁺IL-21⁺ Tfh cells and tertiary lymphoid structures (TLS). TLS formation decreased tumor growth in a CD4⁺ T cell and CXCL13-dependent manner. The transfer of Tfh cells, but not naive CD4⁺ T cells, induced TLS at tumor beds and decreased tumor growth. Thus, TGF-β-mediated silencing of Satb1 licenses Tfh cell differentiation, providing insight into the genesis of TLS within tumors.

IgA transcytosis and antigen recognition govern ovarian cancer immunity

Most ovarian cancers are infiltrated by prognostically relevant activated T cells^1–3, yet exhibit low response rates to immune checkpoint inhibitors⁴. Memory B cell and plasma cell infiltrates have previously been associated with better outcomes in ovarian cancer^5,6, but the nature and functional relevance of these responses are controversial. Here, using 3 independent cohorts that in total comprise 534 patients with high-grade serous ovarian cancer, we show that robust, protective humoral responses are dominated by the production of polyclonal IgA, which binds to polymeric IgA receptors that are universally expressed on ovarian cancer cells. Notably, tumour B-cell-derived IgA redirects myeloid cells against extracellular oncogenic drivers, which causes tumour cell death. In addition, IgA transcytosis through malignant epithelial cells elicits transcriptional changes that antagonize the RAS pathway and sensitize tumour cells to cytolytic killing by T cells, which also contributes to hindering malignant progression. Thus, tumour-antigen-specific and -antigen-independent IgA responses antagonize the growth of ovarian cancer by governing coordinated tumour cell, T cell and B cell responses. These findings provide a platform for identifying targets that are spontaneously recognized by intratumoural B-cell-derived antibodies, and suggest that immunotherapies that augment B cell responses may be more effective than approaches that focus on T cells, particularly for malignancies that are resistant to checkpoint inhibitors.

In patients with high-grade serous ovarian cancer, robust and protective humoral responses are dominated by B-cell-derived polyclonal IgA that binds to polymeric IgA receptors that are universally expressed on ovarian cancer cells.

Methyltransferase inhibitors restore SATB1 protective activity against cutaneous T cell lymphoma in mice

Cutaneous T cell lymphoma (CTCL) has a poorly understood etiology and no known cure. Using conditional knockout mice, we found that ablation of the genomic organizer special AT-rich sequence-binding protein 1 (Satb1) caused malignant transformation of mature, skin-homing, Notch-activated CD4+ and CD8+ T cells into progressively fatal lymphoma. Mechanistically, Satb1 restrained Stat5 phosphorylation and the expression of skin-homing chemokine receptors in mature T cells. Notably, methyltransferase-dependent epigenetic repression of SATB1 was universally found in human Sézary syndrome, but not in other peripheral T cell malignancies. H3K27 and H3K9 trimethylation occluded the SATB1 promoter in Sézary cells, while inhibition of SUV39H1/2 methyltransferases (unlike EZH2 inhibition) restored protective SATB1 expression and selectively abrogated the growth of primary Sézary cells more effectively than romidepsin. Therefore, inhibition of methyltransferases that silence SATB1 could address an unmet need for patients with mycosis fungoides/Sézary syndrome, a set of incurable diseases.

BTN3A1 governs antitumor responses by coordinating αβ and γδ T cells

Gamma delta (γδ) T cells infiltrate most human tumors, but current immunotherapies fail to exploit their in situ major histocompatibility complex-independent tumoricidal potential. Activation of γδ T cells can be elicited by butyrophilin and butyrophilin-like molecules that are structurally similar to the immunosuppressive B7 family members, yet how they regulate and coordinate αβ and γδ T cell responses remains unknown. Here, we report that the butyrophilin BTN3A1 inhibits tumor-reactive αβ T cell receptor activation by preventing segregation of N-glycosylated CD45 from the immune synapse. Notably, CD277-specific antibodies elicit coordinated restoration of αβ T cell effector activity and BTN2A1-dependent γδ lymphocyte cytotoxicity against BTN3A1⁺ cancer cells, abrogating malignant progression. Targeting BTN3A1 therefore orchestrates cooperative killing of established tumors by αβ and γδ T cells and may present a treatment strategy for tumors resistant to existing immunotherapies.

Immune pressure against ovarian cancer depends on antigen-specific CD69+CD103+TRM T cells

The relationship between stem-like, tissue resident memory (TRM) and exhausted T cells at tumor beds is incompletely understood. We found that more than 50% of the CD8+ T cells in human ovarian carcinomas are TRM cells. RNA seq of TRM and their re-circulating counterparts infiltrating multiple human ovarian carcinomas showed a very distinctive phenotype, characterized by co-upregulation of effector and exhaustion markers, along with increased clonality and marked proliferative and lipid metabolism signatures. Interestingly, both populations showed very little overlap in TCR repertoire. Single cell analysis of TRM population showed that this is a heterogeneous population composed of different clusters defined by gene expression and TCR repertoire. A distinctive cluster shows higher expression of cytotoxic mediators and exhaustion markers, along with higher clonality and higher proliferation rate, with a TCR repertoire shared by CD103+TCF7+ stem-like cells. Single cell ATACseq showed that TRM and their counterpart have different chromatin structure and, within both populations also appear variables epigenetic landscapes. In addition, the presence of TRM is correlated with better prognosis, while tumor antigen-specific TRM T cells transferred into syngeneic tumor-bearing mice were more effective at delaying tumor growth than their tumor antigen-specific re-circulating counterparts. Together, our data indicate that productive immune pressure against malignant progression depends on a subset of CD8+ stem-like T cells differentiating into a narrow cluster of TRM T cells of ~300 TCR clones, which represent true tumor antigen-specific effector lymphocytes.

Satb1 deficiency licenses TFH-differentiation and Tertiary Lymphoid Structure formation in cancer

Tertiary Lymphoid Structures (TLS) are commonly identified in human tumors with improved outcome, but how they are orchestrated remains elusive. Here we show that silencing of the master genomic organizer Satb1 results in enhanced antigen-specific T Follicular Helper (TFH) differentiation. Increased TFH thereby promoted antigen-specific intra-tumoral CD19+B220+ B cell responses and spontaneous TLS assembly upon ovarian tumor challenge. Mechanistically, Satb1 deficiency drives increased TFH formation through de-repression of ICOS and PD-1. Accordingly, TGF-β1-driven downregulation of Satb1 licenses activated human CD4+ T-cells for enhanced antigen-specific T Follicular Helper (TFH) differentiation. Furthermore, Satb1 deficiency abrogates the generation of PD-1highCXCR5+Foxp3+ T Follicular Regulatory (TFR) cells during the TFH differentiation process. Importantly, functional TFH cell accumulation, in the absence of Satb1 specifically in CD4+ T cells, resulted in corresponding isotype-switched B cell responses and spontaneous formation of TLS, while B cell depletion accelerated malignant progression. Our results indicate that the formation of TLS in cancer depends on enhanced B cell responses driven by TFH cells generated through Satb1 down-regulation.

SATB1 as a novel therapeutic target for methyltransferase inhibitors against Cutaneous T Cell Lymphoma

Cutaneous T cell lymphoma (CTCL) is a clinically unmet need. Using conditional knockout mice, we found that ablation of the genomic organizer Special AT rich sequence binding protein 1 (Satb1) induces a progressively fatal lymphoma characterized by mature, skin homing, Notch activated CD4 and CD8 T cells. Mechanistically, Satb1 restrains Stat5 phosphorylation and the expression of skin homing chemokine receptors in mature T cells. Notably, SUV39H1 and 2 methyltransferase dependent epigenetic repression of SATB1 is universally found in human Sezary Syndrome, but not other peripheral T cell malignancies. Accordingly, H3K27 and H3K9 trimethylation occlude the SATB1 promoter in Sezary cells. Inhibition of SUV39H1 and 2 methyltransferases with novel drugs, unlike EZH2 inhibition, restores SATB1 expression, selectively abrogating the growth of primary Sezary cells more effectively than Romidepsin. Therefore, SATB1 acts as a tumor suppressor in mature T cells upon NOTCH1 deregulation, and inhibition of methyltransferases that silence SATB1 could address an unmet need for patients with mycosis fungoides and Sezary syndrome.

Butyrophilin 3A1 is a Dynamic T Cell Regulator in Ovarian Cancer

Ovarian carcinoma microenvironmental T cells exert clinically relevant pressure against malignant progression; however current immunotherapies rarely induce ovarian cancer regression. Here we investigate CD277-containing butyrophilin 3A1 (BTN3A1), a poorly investigated immunoregulatory pathway driven by myeloid and tumor cells in ovarian tumor beds. We show that BTN3A1 is overexpressed in ovarian cancer and is associated with a significant survival disadvantage in these patients (n=200). Concomitantly, ectopic expression of BTN3A1 on APCs inhibits αβ T cell proliferation and Th1 cytokine production. Proteomic analyses and binding assays demonstrate that BTN3A1 interacts with the CD45 phosphatase and elements of the TCR. Consequently, TCR ligation in the presence of BTN3A1 inhibits the segregation of CD45 from the immune synapse and blunts downstream signaling by antagonizing the phosphorylation of CD3Zeta, Lck, and Zap70. We developed fully human αCD277 antibodies which rescue αβ T cell proliferation and Th1 cytokine responses, while driving the infiltration of T cells into tumor beds, delaying ovarian tumor progression in novel BTN3A1+ humanized mice and xenograft studies. Paradoxically, αCD277 antibodies promote the activation of γδ T cells by driving a conformational transformation of BTN3A1. Thus, co-transfer of γδ and Ag-specific αβ T cells in the presence of αCD277 antibodies synergize to further impair malignant progression in vivo. Overall, we show that BTN3A1 drives αβ T cell dysfunction in ovarian cancer, while αCD277 antibodies transform this molecule from immunosuppressive to immunostimulatory by rescuing αβ T cells and activating γδ T cells, thus dynamically unleashing T cell-driven antitumor immunity.

Satb1 deficiency licenses TFH-differentiation

T Follicular Helper cells (TFH) provide both co-stimulation and stimulatory cytokines to B cells to facilitate affinity maturation, class switch recombination, and plasma cell differentiation within the germinal center. However, is not clear how TFH differentiation is regulated. We found that deficiency of the chromatin organizer Satb1 results in increased TFH formation in CD4Cre+Satb1flx/flx mice through up-regulation of the canonical TFH markers ICOS and PD-1 and suppression of Foxp3+PD-1highCXCR5+ T follicular regulatory (TFR) cells as well. Accordingly, CD4Cre+Satb1flx/flx mice, or RAG1−/− mice transferred with Satb1-deficient CD4+ T cells showed a dramatic accumulation of CD4+CXCR5+PD-1high upon ovarian tumor challenge, compared to their Satb1+ counterparts, which was associated with reduced tumor growth. Importantly, intratumoral administration of Satb1-deficient CD4+ T cells re-directed to target ovarian cancer cells through chimeric receptors, but not their Satb1+ counterparts, induce the formation of Tertiary Lymphoid Structures in most tumors.

Conclusion

Satb1 controls three mechanisms relevant for TFH differentiation and, subsequently, antigen-specific humoral responses; namely, PD- 1 expression, ICOS de-repression and TFR formation. Our results suggest a novel role for Satb1 as a major regulator of TFH differentiation and TLS during tumor formation.

Frontline Science: Microbiota reconstitution restores intestinal integrity after cisplatin therapy

Due to their cytotoxic activities, many anticancer drugs cause extensive damage to the intestinal mucosa and have antibiotic activities. Here, we show that cisplatin induces significant changes in the repertoire of intestinal commensal bacteria that exacerbate mucosal damage. Restoration of the microbiota through fecal-pellet gavage drives healing of cisplatin-induced intestinal damage. Bacterial translocation to the blood stream is correspondingly abrogated, resulting in a significant reduction in systemic inflammation, as evidenced by decreased serum IL-6 and reduced mobilization of granulocytes. Mechanistically, reversal of dysbiosis in response to fecal gavage results in the production of protective mucins and mobilization of CD11b+ myeloid cells to the intestinal mucosa, which promotes angiogenesis. Administration of Ruminococcus gnavus, a bacterial strain selectively depleted by cisplatin treatment, could only partially restore the integrity of the intestinal mucosa and reduce systemic inflammation, without measurable increases in the accumulation of mucin proteins. Together, our results indicate that reconstitution of the full repertoire of intestinal bacteria altered by cisplatin treatment accelerates healing of the intestinal epithelium and ameliorates systemic inflammation. Therefore, fecal microbiota transplant could paradoxically prevent life-threatening bacteremia in cancer patients treated with chemotherapy.

Genomes of ubiquitous marine and hypersaline Hydrogenovibrio, Thiomicrorhabdus and Thiomicrospira spp. encode a diversity of mechanisms to sustain chemolithoautotrophy in heterogeneous environments

Chemolithoautotrophic bacteria from the genera Hydrogenovibrio, Thiomicrorhabdus and Thiomicrospira are common, sometimes dominant, isolates from sulfidic habitats including hydrothermal vents, soda and salt lakes and marine sediments. Their genome sequences confirm their membership in a deeply branching clade of the Gammaproteobacteria. Several adaptations to heterogeneous habitats are apparent. Their genomes include large numbers of genes for sensing and responding to their environment (EAL- and GGDEF-domain proteins and methyl-accepting chemotaxis proteins) despite their small sizes (2.1-3.1 Mbp). An array of sulfur-oxidizing complexes are encoded, likely to facilitate these organisms' use of multiple forms of reduced sulfur as electron donors. Hydrogenase genes are present in some taxa, including group 1d and 2b hydrogenases in Hydrogenovibrio marinus and H. thermophilus MA2-6, acquired via horizontal gene transfer. In addition to high-affinity cbb₃ cytochrome c oxidase, some also encode cytochrome bd-type quinol oxidase or ba₃ -type cytochrome c oxidase, which could facilitate growth under different oxygen tensions, or maintain redox balance. Carboxysome operons are present in most, with genes downstream encoding transporters from four evolutionarily distinct families, which may act with the carboxysomes to form CO₂ concentrating mechanisms. These adaptations to habitat variability likely contribute to the cosmopolitan distribution of these organisms.