Myoungjoo V. Kim

The cellular and molecular origin of tumor-associated macrophages

Long recognized as an evolutionarily ancient cell type involved in tissue homeostasis and immune defense against pathogens, macrophages are being rediscovered as regulators of several diseases, including cancer. Here we show that in mice, mammary tumor growth induces the accumulation of tumor-associated macrophages (TAMs) that are phenotypically and functionally distinct from mammary tissue macrophages (MTMs). TAMs express the adhesion molecule Vcam1 and proliferate upon their differentiation from inflammatory monocytes, but do not exhibit an “alternatively activated” phenotype. TAM terminal differentiation depends on the transcriptional regulator of Notch signaling, RBPJ; and TAM, but not MTM, depletion restores tumor-infiltrating cytotoxic T cell responses and suppresses tumor growth. These findings reveal the ontogeny of TAMs and a discrete tumor-elicited inflammatory response, which may provide new opportunities for cancer immunotherapy. Origins of tumor macrophages To help the immune system fight cancer, it is important to understand the origins and functions of immune cells in tumors and the surrounding tissues. One type of immune cells, macrophages, is present both in tumors and in nearby noncancerous tissue, but the relationship between these two cell populations is unclear. Franklin et al. found that tumor-associated macrophages in mouse mammaries differed in form, function, and origin from macrophages found in nearby noncancerous mammary tissue. Moreover, when they removed macrophages from the tumors but not the other mammary tissue, tumors shrank and cytotoxic T cells—another kind of immune cell that kills tumor cells—infiltrated the tumors. Tumor-associated macrophages may thus be an important therapeutic target. Science, this issue p. 921. The origins of tumor-associated macrophages in a mouse mammary tumor model are revealed. [Also see Perspective by Perdiguero and Geissmann]

Novel Foxo1-dependent transcriptional programs control T reg cell function

Regulatory T (Treg) cells, characterized by expression of the transcription factor forkhead box P3 (Foxp3), maintain immune homeostasis by suppressing self-destructive immune responses. Foxp3 operates as a late-acting differentiation factor controlling Treg cell homeostasis and function, whereas the early Treg-cell-lineage commitment is regulated by the Akt kinase and the forkhead box O (Foxo) family of transcription factors. However, whether Foxo proteins act beyond the Treg-cell-commitment stage to control Treg cell homeostasis and function remains largely unexplored. Here we show that Foxo1 is a pivotal regulator of Treg cell function. Treg cells express high amounts of Foxo1 and display reduced T-cell-receptor-induced Akt activation, Foxo1 phosphorylation and Foxo1 nuclear exclusion. Mice with Treg-cell-specific deletion of Foxo1 develop a fatal inflammatory disorder similar in severity to that seen in Foxp3-deficient mice, but without the loss of Treg cells. Genome-wide analysis of Foxo1 binding sites reveals ∼300 Foxo1-bound target genes, including the pro-inflammatory cytokine Ifng, that do not seem to be directly regulated by Foxp3. These findings show that the evolutionarily ancient Akt–Foxo1 signalling module controls a novel genetic program indispensable for Treg cell function.

Combination CTLA-4 Blockade and 4-1BB Activation Enhances Tumor Rejection by Increasing T-Cell Infiltration, Proliferation, and Cytokine Production

Background The co-inhibitory receptor Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4) attenuates immune responses and prevent autoimmunity, however, tumors exploit this pathway to evade the host T-cell response. The T-cell co-stimulatory receptor 4-1BB is transiently upregulated on T-cells following activation and increases their proliferation and inflammatory cytokine production when engaged. Antibodies which block CTLA-4 or which activate 4-1BB can promote the rejection of some murine tumors, but fail to cure poorly immunogenic tumors like B16 melanoma as single agents. Methodology/Principal Findings We find that combining αCTLA-4 and α4-1BB antibodies in the context of a Flt3-ligand, but not a GM-CSF, based B16 melanoma vaccine promoted synergistic levels of tumor rejection. 4-1BB activation elicited strong infiltration of CD8+ T-cells into the tumor and drove the proliferation of these cells, while CTLA-4 blockade did the same for CD4+ effector T-cells. Anti-4-1BB also depressed regulatory T-cell infiltration of tumors. 4-1BB activation strongly stimulated inflammatory cytokine production in the vaccine and tumor draining lymph nodes and in the tumor itself. The addition of CTLA-4 blockade further increased IFN-γ production from CD4+ effector T-cells in the vaccine draining node and the tumor. Anti 4-1BB treatment, with or without CTLA-4 blockade, induced approximately 75% of CD8+ and 45% of CD4+ effector T-cells in the tumor to express the killer cell lectin-like receptor G1 (KLRG1). Tumors treated with combination antibody therapy showed 1.7-fold greater infiltration by these KLRG1+CD4+ effector T-cells than did those treated with α4-1BB alone. Conclusions/Significance This study shows that combining T-cell co-inhibitory blockade with αCTLA-4 and active co-stimulation with α4-1BB promotes rejection of B16 melanoma in the context of a suitable vaccine. In addition, we identify KLRG1 as a useful marker for monitoring the anti-tumor immune response elicited by this therapy. These findings should aid in the design of future trials for the immunotherapy of melanoma.

Systemic 4-1BB activation induces a novel T cell phenotype driven by high expression of Eomesodermin

Anti–4-1BB treatment of tumor-bearing or intracellular pathogen infected mice generates a population of Eomes+KLRG1+ tumor infiltrating T cells that have enhanced cytotoxic activity.

The Transcription Factor Foxo1 Controls Central-Memory CD8+ T Cell Responses to Infection

Memory T cells protect hosts from pathogen reinfection, but how these cells emerge from a pool of antigen-experienced T cells is unclear. Here, we show that mice lacking the transcription factor Foxo1 in activated CD8+ T cells have defective secondary, but not primary, responses to Listeria monocytogenes infection. Compared to short-lived effector T cells, memory-precursor T cells expressed higher amounts of Foxo1, which promoted their generation and maintenance. Chromatin immunoprecipitation sequencing revealed the transcription factor Tcf7 and the chemokine receptor Ccr7 as Foxo1-bound target genes, which have critical functions in central-memory T cell differentiation and trafficking. These findings demonstrate that Foxo1 is selectively incorporated into the genetic program that regulates memory CD8+ T cell responses to infection.

miR-182 Is Largely Dispensable for Adaptive Immunity: Lack of Correlation between Expression and Function

MicroRNA (miR)-mediated regulation of protein abundance is a pervasive mechanism of directing cellular processes. The well-studied and abundant miR-182 has previously been implicated in many aspects of T cell function, DNA repair, and cancer. In this study, we show that miR-182 is the most highly induced miR in B cells undergoing class-switch recombination. To elucidate the requirement of miR-182 in lymphocyte function, we extensively characterized mice with a targeted deletion of Mir182. We show that despite its dramatic induction, loss of miR-182 has minimal impact on B cell development, the ability of B cells to undergo class-switch recombination ex vivo and to undergo Ag-driven affinity maturation in vivo. Furthermore, in striking contrast to knockdown studies that demonstrated the requirement of miR-182 in T cell function, miR-182–deficient mice display no defect in T cell development and activation. Finally, we show that T cell–dependent immune response to experimental Listeria monocytogenes infection is intact in miR-182–deficient mice. We conclude that, contrary to previous studies, miR-182 does not play a significant role in all measured aspects of mouse adaptive immunity. This striking absence of a phenotype highlights the lack of correlation between expression pattern and functional requirement, underscores the limitations of using knockdown approaches to assess miR requirements, and suggests that miR networks may compensate for the chronic loss of specific miRs.