Weekly Digests
‹ Back to January

You can’t kill what you can't find: dormant disseminated tumor cells (DTCs) evade T cells through “relative scarcity”

January 17, 2024

Surviving breast cancer is an incredible feat, but patients whose initial tumors are successfully cleared still face a high risk of recurrence, even years after initial treatment. Tumor recurrence can be attributed to the presence of dormant disseminated tumor cells (DTCs) that hide out in the body and can potentially seed new tumors later on. In recent work published in Cancer Cell, Goddard et al. investigated just how these sneaky cells evade the immune system, and found that it may just come down to a numbers game.

To begin, Goddard et al. established two models of DTCs. In the first model, parental 4T1 or 4TO7 mammary tumor cells, or the same cells engineered to express a dominant eGFP neoantigen and firefly luciferase, were transplanted into Balb/c mice. While tumors expressing the dominant neoantigens were spontaneously rejected by endogenous antigen-specific T cells, which were present in the spleens, lymph nodes, and bone marrow, eGFP+ DTCs remained in the bone marrow, evading antitumor immunity. This did not appear to be due to T cell exhaustion or dysfunction, as antigen-specific T cells remained active, functional, and capable of expanding and protecting mice upon rechallenge. In the second model, D2.0R mammary tumor cells expressing eGFP were intravenously administered to Balb/c mice. D2.0R cells persisted as solitary cells or small non-proliferative clusters within the lungs through day 240, despite the presence of antigen-specific T cells.

Comparing the D2.0R-eGFP model, which seeds dormant micrometastases, to another model, D2A1, which seeds proliferative metastases, the researchers noted downregulation of B2m, (a critical component of MHC-I that is essential for antigen presentation) over time in the D2.0R-eGFP cells. MHC-I was also downregulated at the protein level in these cells, suggesting a possible mechanism of immune evasion. Despite reduced MHC-I expression in D2.0R-eGFP DTCs, the levels of MHC-I expressed in proliferating and non-proliferating D2A1 cells were similar, suggesting that MHC-I downregulation was not linked to quiescence. It was also not due to selective pressure from the adaptive immune system, as similar patterns were observed in T cell-deficient athymic mice.

To determine whether the extent of the MHC-I downregulation would actually be sufficient for DTCs to evade antitumor T cells, the researchers developed microvascular niche (MVN) culture systems that, depending on the culture, could drive T4-2 breast cancer cells towards their typical proliferative state, or towards a quiescent state that mimicked the phenotype of MHC-I downregulation by quiescent DTCs observed in mice. Using these systems to co-culture T4-2 cells engineered to express NY-ESO-1 alongside HLA-A2/NY-ESO-1-specific TCR T cells, the researchers found that the T cells eliminated most of the target cells, regardless of whether they were proliferative or quiescent. Testing the same concept in vivo, the researchers transplanted mice with syngeneic D2.0R-eGFP cells expressing influenza virus hemaglutinin (HA), which can be recognized by adoptively transferred CL4 TCR CD8+ T cells. Again, despite reduced expression of MHC-I, the tumor cells could be recognized and significantly cleared, suggesting that the level of MHC-I downregulation by DTCs was not sufficient to escape detection by antigen-specific CD8+ T cells.

Goddard et al. hypothesized that CL4 TCR T had likely cleared the DTCs with higher MHC-I expression, leaving only those with lower MHC-I expression, but analysis showed that persistent DTCs maintained a full spectrum of MHC-I expression levels. Further, when the researchers treated mice harboring residual DTCs with IFNγ, upregulating MHC-I expression, DTCs still persisted in the presence of either endogenous T cells or adoptively transferred TCR T cells. These results further suggest that reduced MHC-I expression is not the driving mechanism behind DTC immune evasion.

Following observations that adoptive transfer of high volumes of antigen-specific T cells could be sufficient for DTC clearance, the researchers investigated the possibility that DTCs may evade immune detection simply due to limited interactions between the two relatively rare cell types. To study this mechanism of “relative scarcity”, the researchers used T cell-deficient AtN mice seeded with D2.0R-eGFP DTCs and transferred eGFP-specific JEDI T cells in log-fold dilutions. This showed a dose-dependent clearance of DTCs. As expected, the average distance between T cells and DCs also decreased with higher doses of T cells. Similarly, a T cell-based vaccination system that elicited expansion of endogenous CD8+ T cells against target antigens reduced dormant DTCs.

To test whether CAR T cells could clear DTCs, Goddard et al. used T4-2 breast cancer cells engineered to express a modified CD19 with no signal transduction capacity in coculture with CD19 CAR T cells. Here, the researchers saw a 93% reduction in both proliferating and quiescent target cells. For in vivo studies, the team used mice seeded with tCD19+ D2.0R cells and treated them with CD19 CAR T cells. This eliminated an average of 98% of DTCs in mouse lungs, outperforming the previous studies with tumor antigen-specific T cells. Similar results were observed using CAR T cells targeting the known breast cancer antigen HER2 in mice bearing HER2+ BT474 or HCC1569 human breast cancer lines, which can become proliferative or dormant depending on their location in the body. A mouse-optimized version of a trastuzumab-based CAR construct currently under clinical investigation was also effective at clearing DTCs.

Overall, these results show that while DTCs downregulate MHC-I, they primarily evade immune detection through “relative scarcity” – limited interactions between DTCs and the T cells that might recognize them. Immunotherapies that increase T cells specific for a known DTC antigen, like vaccination or the adoptive transfer of TCR-engineered or CAR T cells, can help to overcome relative scarcity, clearing DTCs that might potentiate tumor recurrence.

Write-up and image by Lauren Hitchings


Goddard ET, Linde MH, Srivastava S, Klug G, Shabaneh TB, Iannone S, Grzelak CA, Marsh S, Riggio AI, Shor RE, Linde IL, Guerrero M, Veatch JR, Snyder AG, Welm AL, Riddell SR, Ghajar CM. Immune evasion of dormant disseminated tumor cells is due to their scarcity and can be overcome by T cell immunotherapies. Cancer Cell. 2024 Jan 8.

In the Spotlight...

CD4+ T cell immunity is dependent on an intrinsic stem-like program

Zou et al. demonstrated that naive alloantigen-specific CD4+ T cells mainly develop into TCF1+Ly108+ effector precursor (TEP) cells and TCF1CXCR6+ effectors in response to heart transplantation. Adoptive transfer of TCF1+ stem-like CD4+ TEP cells, but not TCF1 CD4+ effector cells, induced transplant rejection. Mechanistically, TCF1 sustained the self-renewal potential of CD4+ TEP cells, while IRF4 governed their differentiation into effector cells. scRNAseq analysis further identified LDHA as a crucial regulator of CD4+ TEP cell differentiation. In the absence of IRF4 or LDHA, CD4+ TEP cells failed to differentiate into TCF1CXCR6+ effector cells, leading to transplant acceptance.

Contributed by Shishir Pant

Distinct spatiotemporal dynamics of CD8+ T cell-derived cytokines in the tumor microenvironment

Hoekstra and Slagter et al. studied the spatiotemporal behaviors of CD8+ T cell-derived IFNγ and TNFα in the TME. Using a single-cell transcriptome-based approach designed to identify cytokines signals received over time, they showed in both humanized and syngeneic mouse models that IFNγ was the dominant modifier of the TME, acting globally, compared with TNFα, which had short-range effects. In addition, T cell-exposed tumors with a strong IFNγ profile had decreased expression of TGFβ-induced genes, indicative of TME remodeling, providing evidence that the approach could be useful to dissect local and global cytokine modulation in the TME.

Contributed by Katherine Turner

IL-12 reprograms CAR-expressing natural killer T cells to long-lived Th1-polarized cells with potent antitumor activity

Landoni et al. showed that IL-12-transduced human blood NKT cells were Th1 polarized and polyfunctional, overexpressed activation and memory (CD62L) markers, and had autocrine/ paracrine IL-12 activity and increased proliferation upon stimulation. IL-12 stimulated de novo CD62L expression and proliferative responses in CD62L+ and CD62L- untransduced NKT. IL-12+ NKT cells engrafted in mice retained CD62L expression and had greater expansion and persistence than controls. IL-12 co-expression, either soluble or membrane-bound, boosted CAR-NKT cell CD62L expression, Th1 polarization, and antitumor activity in vitro and in leukemia and neuroblastoma mouse models.

Contributed by Paula Hochman

Single-cell and spatial profiling identify three response trajectories to pembrolizumab and radiation therapy in triple negative breast cancer

Shiao et al. profiled longitudinal biopsies from patients with TNBC using scRNAseq and multiplex IHC with spatial analysis (CODEX) to elucidate the immune response to PD-1 therapy in combination with radiotherapy (RT). Two responder (R1 and R2) and one non-responder (NR) patterns were identified. R1 exhibited high immune infiltrates at baseline and a vigorous T cell response after pembrolizumab. R2 had low immune infiltrates (similar to NR) at baseline, but showed delayed response after pembrolizumab and RT, similar to an orthotopic E0771 murine model of TNBC. NR showed low MHC class I/II expression at baseline and didn’t respond despite treatment.

Contributed by Shishir Pant

T-cell stimulating vaccines empower CD3 bispecific antibody therapy in solid tumors

To improve the efficacy of CD3 bispecific antibodies (bsAb) in immunologically “cold” solid tumors, Middelburg et al. used various vaccine formulations (long peptides adjuvanted with imiquimod and IL-2 or CpG, or virus-based) to induce activation and influx of peripheral T cells into tumors. Vaccine-recruited CD8+ T cells served as critical effector cells for subsequently administered CD3 bsAb, and the addition of CD3 bsAb facilitated deeper infiltration of T cells into the tumor center. The combination treatment, even with vaccines that did not contain relevant tumor antigens, induced a broadly inflamed Th1 tumor microenvironment and resulted in improved antitumor activity.

Contributed by Ute Burkhardt

Therapeutic application of human type 2 innate lymphoid cells via induction of granzyme B-mediated tumor cell death

Li, Ma, Tang, et al. developed a technique to study human group 2 innate lymphoid cell (ILC2) functions by expanding blood-obtained ILC2 ex vivo (ex ILC2s). Ex ILC2s were at an intermediate activation state and maintained the ILC2 phenotype. Ex ILC2 were able to kill AML cells in vitro and control tumor growth in AML mouse models. ILC2-mediated tumor killing was dependent on DNAM-1 interacting with its ligands, CD122 and CD155, which led to downstream inactivation of FOXO1 and production of granzyme B, triggering apoptosis or pyroptosis. High tumoral CD155 levels suppressed DNAM-1 on ILC2, resulting in immune evasion. ILC2s also had potential antitumor activity against solid tumors.

Contributed by Maartje Wouters

Everything New this Week In...

Close Modal

Small change for you. Big change for us!

This Thanksgiving season, show your support for cancer research by donating your change.

In less than a minute, link your credit card with our partner RoundUp App.

Every purchase you make with that card will be rounded up and the change will be donated to ACIR.

All transactions are securely made through Stripe.