Immune checkpoint blockade, or ICB, has transformed cancer treatment by releasing molecular brakes that restrain T cells. Drugs that block proteins such as PD-1, PD-L1 or CTLA-4 can restore the ability of T cells to recognize and attack malignant cells, producing long-lasting responses in some people with cancer. Yet the treatment does not work uniformly. Its success depends on a chain of events in which tumor antigens are captured, processed and displayed to T cells by antigen-presenting cells, particularly dendritic cells. Among these, conventional type 1 dendritic cells, known as cDC1s, have attracted intense attention because they are highly effective at cross-presenting tumor-derived proteins on major histocompatibility complex class I molecules, a process that activates tumor-killing CD8-positive T cells.

The new work examined whether cDC1s are absolutely required for ICB to eliminate a primary tumor. To do so, the researchers used mice carrying an immunogenic clone of Lewis lung carcinoma, or LLC, a transplantable mouse tumor model. They compared normal animals with genetically modified Batf3-deficient mice. The Batf3 transcription factor is necessary for the development of cDC1s, so Batf3-knockout animals lack this dendritic-cell subset. In normal mice, most animals rejected the LLC tumors after receiving ICB. Surprisingly, the treatment also triggered tumor rejection in 35.7 percent of the Batf3-deficient mice. The result indicates that, at least for this immunogenic LLC tumor, alternative antigen-presenting cells can support an initial antitumor response when cDC1s are absent.

That alternative route appears to involve XCR1-negative antigen-presenting cells. XCR1 is a chemokine receptor associated with cDC1s, making it a useful marker for distinguishing these cells from other antigen-presenting populations. After ICB, the researchers observed increased expression of costimulatory molecules on XCR1-negative APCs in both tumors and draining lymph nodes of Batf3-deficient mice. Costimulatory molecules such as CD40 and CD80 provide essential secondary signals during T-cell activation. Antigen recognition alone is often insufficient; without costimulation, T cells may become inactive or tolerant. The observed increase in CD40 and CD80 suggests that non-cDC1 APCs were not merely present but were being functionally activated in response to checkpoint therapy.

The researchers then investigated why the LLC model could provoke this backup immune pathway while another tumor model, the B16F10 melanoma, remained resistant to ICB. They collected conditioned culture media—the fluid containing molecules secreted by tumor cells—from LLC and B16F10 cultures and exposed bone-marrow-derived dendritic cells to it. Media from LLC cells stimulated both cDC1s and cDC2s, another conventional dendritic-cell subset, causing increased expression of CD40 and CD80. Media from ICB-resistant B16F10 cells did not produce the same effect. This experiment points to soluble factors released by the tumor microenvironment as potential drivers of dendritic-cell activation. The molecules were not identified in the study, but the contrast suggests that tumor cells can differ substantially in their ability to alert and organize immune responses.

To explore that difference at the molecular level, the team performed RNA sequencing on LLC and B16F10 tumor cells. The analysis showed that genes linked to antitumor immunity were more strongly expressed in LLC cells than in B16F10 cells. Such genes could influence how tumor antigens are released, how inflammatory signals are generated or how immune cells are recruited and activated. A tumor that produces the right combination of danger signals may effectively condition multiple APC populations, creating redundancy in the pathway leading to T-cell activation. By contrast, an immune-cold tumor such as B16F10 may fail at several points: it may present fewer recognizable antigens, release weaker activating signals or actively suppress the cells that would otherwise initiate immunity.

The most consequential finding emerged when the researchers tested immune memory. Mice that had become tumor-free after ICB were later exposed again to LLC tumors, a standard rechallenge experiment designed to determine whether the initial response created protective immunological memory. In Batf3-deficient animals that had rejected their primary tumors without cDC1 supplementation, the rechallenged tumors were not spontaneously eliminated. In other words, the mice could mount a successful first attack but did not retain a sufficiently powerful memory response to repel the same tumor a second time. This distinction is biologically important. Primary rejection can rely on a temporary or locally organized immune response, whereas durable memory requires the generation, survival and later reactivation of specialized T-cell populations, processes that depend on precise antigen presentation and coordination among immune cells.

The findings support a two-stage model of checkpoint immunotherapy. During the first stage, activated XCR1-negative APCs, including cDC2-like populations, may present tumor antigens and provide costimulation strong enough to initiate T-cell-mediated destruction. These cells could acquire tumor material in the tumor bed or draining lymph nodes, process it and present it to T cells through major histocompatibility complex molecules. Checkpoint blockade would then remove inhibitory signaling, allowing the newly activated T cells to expand and attack the cancer. During the second stage, however, cDC1s may be indispensable for shaping the quality and persistence of the response. Their specialized cross-presentation capacity could help sustain repeated T-cell stimulation, support the development of memory precursor cells and establish long-term surveillance against residual or returning tumor cells.

The work does not mean that cDC1s are unimportant in all cancers, nor does it show that patients lacking a direct equivalent of the mouse pathway would respond in the same way. The experiments used genetically modified mice and transplantable tumor models, and the percentage of Batf3-deficient animals rejecting LLC was substantially lower than the response seen in wild-type mice. The results instead highlight the complexity of immune responses within tumors and the danger of reducing immunotherapy to a single cellular mechanism. Future treatments may need to activate both cDC1-dependent and cDC1-independent pathways: one to generate a forceful initial attack and another to ensure that the immune system remembers what it has defeated. Identifying the soluble tumor-derived signals that activate alternative APCs could help explain why some cancers respond to ICB while others resist it, while strategies that restore or enhance cDC1 function could improve the durability of responses. The study’s central message is therefore both encouraging and cautionary: the immune system may find more than one way to destroy a tumor, but the route to lasting protection is narrower than the route to an initial victory.

The central question is how much of a person’s immune behaviour is encoded in DNA and how much is acquired over time. Although identical twins share nearly all of their genetic sequence, their immune systems can diverge substantially as they encounter different infections, medications, diets, stressors and environmental exposures. Non-identical twins, who share roughly half of their genetic variants on average, will provide an additional comparison group for estimating the contribution of heredity to immune variation.

The investigators will use the Snow Centre’s Cyton2 Cell Timer model to study immune cells dynamically rather than relying only on conventional measurements taken at a single point in time. Standard immune tests often provide a snapshot, such as the number of cells present or the concentration of a signalling molecule. The Cell Timer approach is designed to track cellular activity over time, helping researchers observe when immune cells activate, how long they remain active and when their responses decline.

This temporal information could reveal biological differences that are invisible in a static laboratory result. Two individuals may produce similar numbers of immune cells, for example, while differing in how rapidly those cells respond, how strongly they signal to neighbouring cells or how long inflammation persists. By recording these changing patterns, researchers hope to identify immune-response signatures associated with age, sex and genetic inheritance, as well as signatures shaped by lived experience.

Twin comparisons are particularly valuable because they allow researchers to examine biological variation under partially controlled genetic conditions. If identical twins show similar immune responses despite different life histories, the pattern may indicate a stronger genetic influence. Conversely, marked differences between genetically identical twins may point to environmental exposures, previous infections, medication histories or other factors that have altered immune function. The study will not treat genes and environment as separate forces, however; it will also examine how they interact to shape immune responses.

Dr Lucas Calais-Ferreira, Director of Twins Research Australia, said the project would use these contrasts to estimate how much immune variation is genetic and how much is environmental. Twins Research Australia, based at the University of Melbourne, maintains one of the world’s largest volunteer twin research registries. Its involvement provides access to participants with detailed personal and family histories, allowing immune measurements to be interpreted alongside information about health, age and exposure.

The study is also being informed by the experiences of identical twins Nicole and Amanda Campbell, who have previously participated in research through the registry. Nicole has Crohn’s disease, while Amanda has multiple sclerosis, and both conditions are currently in remission. Their different health histories illustrate how genetically similar people can experience distinct immune-related outcomes and provide a compelling example of the biological questions the new research is designed to address.

Professor Jason Tye-Din, Director of the Snow Centre for Immune Health, described the technology as a shift from taking a still photograph of the immune system to recording a video. That distinction could be important for understanding why one person responds well to a vaccine while another develops stronger side effects, or why a treatment controls inflammation in one patient but proves less effective in another. The researchers hope that identifying the timing and intensity of immune-cell activity will eventually support more accurate predictions of treatment response.

The long-term goal is to contribute to personalised medicine for conditions including type 1 diabetes, rheumatoid arthritis, multiple sclerosis and other immune-related diseases. Better knowledge of individual immune behaviour could help clinicians select treatments more precisely, reduce avoidable side effects and develop prevention strategies tailored to a person’s biological risk. The project may also improve understanding of how immunity changes across the lifespan, potentially clarifying why responses to infections and vaccines differ between younger and older adults.

Recruitment is now seeking identical and non-identical twins aged 18 to 80. By combining longitudinal immune-cell tracking with the natural experimental framework of twin research, the Snow Centre and Twins Research Australia aim to build a more detailed picture of why human immune systems vary—and how that variation can be used to make future healthcare more predictive, targeted and effective.

Subject of Research: People

Article Title: Australian-First Twin Study Tracks Why Immune Responses Differ Between Genetically Similar People

Web References: https://www.twins.org.au; https://snowimmunehealth.org.au

Image Credits: WEHI

Keywords: Twins, immune health, immunology, immune response, personalised medicine, infections, vaccines, autoimmune disease, genetic inheritance, environmental factors, Snow Centre for Immune Health, Twins Research Australia