TEMRA cells are a distinct subset of T cells that have passed through the memory stage of immune development and then re-expressed a surface protein called CD45RA, which is normally found on naïve, inexperienced T cells. The name stands for “terminally differentiated effector memory cells re-expressing CD45RA,” and these cells occupy an unusual immunological niche: they carry the battle scars of prior antigen encounters while wearing a molecular coat that makes them resemble cells that have never fought anything. That paradox hints at their complex biology, which involves potent killing ability, inflammatory signaling, ties to chronic viral infection, and a growing list of connections to aging, autoimmune disease, and cancer.
How TEMRA Cells Are Defined
Immunologists classify T cell subsets by the combination of surface proteins they display. TEMRA cells are identified as CD45RA-positive and CCR7-negative. CD45RA is a marker shared with naïve T cells, but the absence of CCR7 (a receptor that guides cells toward lymph nodes) sets TEMRA cells apart. Most TEMRA cells also lack the co-stimulatory molecules CD27 and CD28, which are gradually lost as T cells undergo repeated rounds of activation. In the CD8+ compartment especially, TEMRA cells frequently express high levels of the cytotoxic molecules granzyme B and perforin, along with the transcription factor T-bet, and the surface marker CD57, which is associated with replicative history and late-stage differentiation.
A study of kidney transplant recipients found that expanded TEMRA populations carried the full CD45RA+CCR7−CD27−CD28− phenotype together with high perforin, granzyme B, T-bet, and the ability to secrete the inflammatory cytokines TNF-α and IFN-γ.1PubMed Central. Expansion of highly differentiated cytotoxic terminally differentiated effector memory CD8+ T cells in a subset of clinically stable kidney transplant recipients: a potential marker for late graft dysfunction CD4+ TEMRA cells share the same CD45RA+CCR7− backbone but can diverge in their cytotoxic toolkit. Some CD4+ TEMRA populations express cytotoxic molecules like GPR56 and granzyme B at very high levels, while others do not, suggesting meaningful heterogeneity even within what looks like a single category.2Nature Communications. Unique phenotypes and clonal expansions of human CD4 effector memory T cells re-expressing CD45RA
Where TEMRA Cells Come From
The name includes “terminally differentiated,” which implies these cells sit at the end of a one-way road. The standard model of T cell differentiation runs from naïve cell to central memory to effector memory, with TEMRA representing the final stop. But the path is not as linear as textbooks once suggested. Research on tumor-infiltrating lymphocytes in non-small-cell lung cancer showed that CD8+ T cells can reach the TEMRA state through at least two divergent trajectories, one of which depends on sustained expression of the co-stimulatory molecules CD27 and CD28 and is linked to weaker T cell receptor engagement.3Journal for ImmunoTherapy of Cancer. CD8+ TILs in NSCLC differentiate into TEMRA via a bifurcated trajectory: deciphering immunogenicity of tumor antigens That finding is important because it means not all TEMRA cells had the same journey, and cells arriving by different routes can have meaningfully different functional properties.
Homeostatic cytokines also play a role. Work on gamma-delta T cells found that TEMRA cells could be generated from central memory cells through IL-15-driven proliferation in the absence of antigen, meaning TEMRA cells do not always require a fresh encounter with a pathogen to form.4PubMed. Differential requirements for antigen or homeostatic cytokines for proliferation and differentiation of human Vgamma9Vdelta2 naive, memory and effector T cell subsets IL-15 responsiveness actually increases progressively from naïve to central memory to effector memory to TEMRA, meaning these cells are especially tuned to survival and maintenance signals from the surrounding tissue.
Cytotoxic Killing Power
The hallmark function of CD8+ TEMRA cells is cytotoxicity. These cells are loaded with the molecular machinery for killing: perforin punches holes in target cell membranes, and granzyme B enters through those holes to trigger cell death from the inside. TEMRA cells also secrete inflammatory cytokines, particularly TNF-α and IFN-γ, which recruit and activate other immune cells. In kidney transplant recipients, TEMRA CD8+ T cells showed enhanced migratory properties compared to other effector memory cells, with greater adhesion to activated blood vessel walls and stronger movement toward the chemokine CXCL12.5PubMed Central. Effector Memory–Expressing CD45RA (TEMRA) CD8+ T Cells from Kidney Transplant Recipients Exhibit Enhanced Purinergic P2X4 Receptor–Dependent Proinflammatory and Migratory Responses That combination of cytotoxicity and tissue-homing ability makes them potent but sometimes destructive.
Without any outside stimulation, TEMRA cells are metabolically more active than naïve or ordinary effector memory cells, running with a high ATP reservoir and elevated activity of several energy-production pathways. When stimulated, they ramp up both sugar metabolism and mitochondrial respiration further.6Frontiers in Immunology. IL-15 Harnesses Pro-inflammatory Function of TEMRA CD8 in Kidney-Transplant Recipients Think of them as idling at a higher RPM than other T cells, ready to redline quickly when needed.
When TEMRA Cells Start Acting Like Natural Killer Cells
One of the more surprising discoveries about TEMRA cells is that some of them acquire features of natural killer (NK) cells, a completely different branch of the immune system. Research published in Nature Immunology found that CD27−CD28− CD8+ T cells (a phenotype overlapping heavily with TEMRA) lost their T cell receptor signaling and instead expressed NKG2D paired with the NK adaptor molecule DAP12. This complex allowed them to kill target cells that displayed NKG2D ligands, regardless of whether those targets carried the specific antigen the T cell originally recognized.7Nature Immunology. Sestrins induce natural killer function in senescent-like CD8+ T cells The molecular drivers behind this shift were stress-response proteins called sestrins, which accumulate in aging or senescent-like T cells.
Cytomegalovirus (CMV) infection appears to accelerate this process. In renal transplant recipients, CMV drove the expansion of TEMRA and CD57+ TEMRA populations that expressed the NK-cell receptors LIR-1 and KLRG1. These cells showed elevated IFN-γ production and enhanced killing capacity against CMV proteins.8PubMed. CMV drives the expansion of highly functional memory T cells expressing NK-cell receptors in renal transplant recipients The result is a cell that blurs the line between adaptive and innate immunity, wielding broad-spectrum killing power instead of the surgical antigen-specific targeting T cells are known for.
The CMV Connection
If one pathogen has been most consistently linked to TEMRA cell expansion, it is cytomegalovirus. CMV is a herpesvirus that infects a large portion of the global population and, after the initial infection clears, remains latent for life. The immune system must constantly patrol for reactivation, and that chronic surveillance appears to push large numbers of CD8+ T cells all the way to the TEMRA state.
In kidney transplant recipients, CMV viremia (detectable virus in the blood) led to significant expansion of CD57+ TEMRA cells.9Human Immunology. Cytomegalovirus-associated CD57+ KLRG1+ CD8+ TEMRA T cells are associated with reduced risk of CMV viremia in kidney transplantation and chronic allograft dysfunction in lung transplantation Meanwhile, in bone marrow, CMV-seropositive individuals accumulated senescent CD8+ TEMRA cells with bright CD45RA expression and high responsiveness to IL-15.10Frontiers in Immunology. Increased IL-15 Production and Accumulation of Highly Differentiated CD8+ Effector/Memory T Cells in the Bone Marrow of Persons with Cytomegalovirus The picture that emerges is that CMV acts as a persistent engine for TEMRA generation, which is relevant because this expansion has downstream consequences for aging, transplant outcomes, and vaccine responses.
TEMRA Cells and Aging
TEMRA cells accumulate with age. Epigenetic profiling has confirmed that these cells increase in older individuals and are elevated further in age-related chronic inflammatory diseases.11PubMed Central. Epigenetic quantification of immunosenescent CD8(+) TEMRA cells in human blood Because TEMRA cells occupy space within the T cell compartment, their expansion can crowd out the naïve T cells needed to respond to new threats. This is one proposed mechanism for why older adults mount weaker responses to new vaccines or infections: the immunological real estate is increasingly occupied by TEMRA cells that are excellent at patrolling for old threats like CMV but not particularly useful against a novel pathogen.12Frontiers in Immunology. The role of TEMRA cell-mediated immune senescence in the development and treatment of HIV disease
A common label for TEMRA cells is “senescent,” but that is an oversimplification. Truly senescent cells are permanently unable to divide. Work on severe asthma patients found that their CD8+ TEMRA cells proliferated at substantially higher rates than TEMRA cells from age-matched controls, with up to 38% of TEMRA cells dividing under stimulation despite expressing classic senescence markers. The researchers concluded these cells were not truly senescent.13PubMed Central. CD8+ TEMRAs in severe asthma associate with asthma symptom duration and escape proliferation arrest So calling all TEMRA cells “senescent” misses the fact that some retain proliferative capacity depending on their context and the disease setting they inhabit.
What TEMRA Cells Mean for Vaccine Responses
The link between TEMRA accumulation and weakened vaccine responses has been tested directly. A study of older adults receiving Moderna’s COVID-19 mRNA vaccine found that overall antibody response was inversely correlated with the level of CD8+CD28− TEMRA cells, even after adjusting for prior COVID-19 infection.14PubMed Central. Frailty impacts immune responses to Moderna COVID-19 mRNA vaccine in older adults In the same cohort, people with milder frailty and fewer CD4+ TEMRA cells tended to mount the strongest helper T cell responses to the vaccine.15PubMed Central. Frailty and age impact immune responses to Moderna COVID-19 mRNA vaccine The practical implication is that TEMRA burden could partly explain why some older adults respond poorly to vaccination, and measuring TEMRA levels might someday help identify who needs modified vaccine strategies.
Roles in Autoimmune Disease
TEMRA cells are not merely bystanders in autoimmune conditions. In systemic lupus erythematosus (SLE), researchers identified a specific CD161−CD8+ TEMRA subpopulation whose expansion was linked to a genetic variant in DTHD1 and was critical to disease pathogenesis.16eBioMedicine. Cytotoxic CD161−CD8+ TEMRA cells contribute to the pathogenesis of systemic lupus erythematosus In rheumatoid arthritis (RA), CD4+ TEMRA cells exhibited cytotoxic T lymphocyte-like functions, prominently expressed the senescence marker p16, and showed reduced T cell receptor diversity, suggesting they had expanded from just a few clones.17Annals of the Rheumatic Diseases. OP0250 COMPREHENSIVE IMMUNOPHENOTYPING REVEALS OLIGOCLONAL EXPANSION OF AUTOREACTIVE T CELLS AND THE ROLE OF IL-6 IN THEIR DIFFERENTIATION IN RHEUMATOID ARTHRITIS Separately, PAD4-specific killer T cells in RA patients carried a TEMRA phenotype marked by CD57, KLRG1, and CD69.18Annals of the Rheumatic Diseases. Anti-PAD4 antibodies link autoimmunity to PAD4 with CTL-associated rheumatoid arthritis
Perhaps most striking from a treatment perspective, RA patients on anti-TNF therapy who failed to achieve remission had significantly higher proportions of both CD4 and CD8 TEMRA cells compared to those who did reach remission. That pattern was specific to anti-TNF treatment and was not seen with methotrexate or abatacept, raising the possibility that TEMRA cells actively interfere with how TNF-blocking drugs work. When patients in remission had their anti-TNF tapered, those who flared showed a rise in CD4+ TEMRA cells, suggesting these cells might serve as a biomarker for relapse risk.19Annals of the Rheumatic Diseases. OP0011 HIGHLY DIFFERENTIATED CD4 AND CD8 T EFFECTOR MEMORY CELLS RE-EXPRESSING CD45RA (TEMRA) ARE ASSOCIATED WITH ACTIVE DISEASE REFRACTORY TO ANTI-TNF THERAPY IN RHEUMATOID ARTHRITIS
The Double-Edged Role in Cancer
In tumors, TEMRA cells present a paradox. On one hand, their cytotoxic arsenal makes them theoretically well-suited to kill cancer cells. A study in colorectal cancer identified a CX3CR1+ CD8+ T cell subset with a TEMRA-like terminal effector phenotype that showed potent cytotoxicity and low exhaustion. Enrichment of these cells independently predicted better overall survival, and effective anti-PD-1 immunotherapy worked in part by promoting the proliferation of this specific population.20Frontiers in Immunology. CX3CR1 identifies a potent effector CD8+ T cell subset associated with anti-PD-1 therapeutic efficacy in colorectal cancer
On the other hand, the tumor microenvironment can push T cells into a dysfunctional TEMRA state. Research found that protein overload within tumors triggers a breakdown in cellular protein-management systems, driving T cells to differentiate into TEMRA cells with senescent-like features, including reduced proliferative capacity. In humanized tumor models, administering amino acids directly into the tumor reduced TEMRA accumulation, boosted T cell proliferation, and improved tumor control.21PubMed Central. Proteostasis Collapse Drives Effector Memory T Cells Re-expressing CD45RA (TEMRA) Generation in the Tumor Microenvironment So the same “TEMRA” label can describe cells that are highly functional tumor killers in one context and burnt-out, senescent-like cells in another. The trajectory matters enormously.
CD4+ Versus CD8+ TEMRA Cells
Most research on TEMRA cells has focused on the CD8+ compartment, where these cells are more abundant. CD4+ TEMRA cells are rarer in healthy people but are increasingly recognized as having distinct and clinically relevant roles. In an aging community cohort, CD4+ TEMRA cells were associated with cognitive impairment on a standard mental status exam, whereas CD8+ TEMRA cells correlated with blood biomarkers of neurodegeneration and brain inflammation but were not linked to cognitive scores themselves.22PubMed Central. Terminally differentiated effector memory T cells associate with cognitive and AD-related biomarkers in an aging-based community cohort That split hints at different biological pathways through which each TEMRA subset might influence brain health.
In chronic prostatitis, single-cell transcriptomics revealed that CD8+ TEMRA cells were enriched for cytokine-mediated signaling pathways and showed elevated TNF signaling, contributing to the inflammatory picture of the disease.23PubMed Central. Characterizing CD8+ TEMRA Cells in CP/CPPS Patients: Insights from Targeted Single-Cell Transcriptomic and Functional Investigations Meanwhile, the RA studies described earlier highlighted CD4+ TEMRA cells as a marker of treatment resistance specifically to anti-TNF therapy. The overall message is that CD4+ and CD8+ TEMRA cells are not interchangeable; they accumulate differently, traffic to different tissues, and associate with different disease outcomes.
Epigenetic Wiring Under the Hood
What locks TEMRA cells into their distinctive identity? A growing body of work points to the chromatin landscape. Using a technique called ATAC-seq that maps which stretches of DNA are physically open or closed in a cell, researchers found that TEMRA cells had lost chromatin accessibility at over 1,300 regions compared to central and effector memory T cells. The regions that closed down in TEMRA cells were rich in binding sites for activation-associated transcription factors like Jun/Fos, NF-κB, and STAT. Meanwhile, the relatively few regions that opened up in TEMRA cells contained binding sites for T-box transcription factors, specifically T-bet and EOMES, which drive cytotoxic gene programs.24Frontiers in Immunology. Cytotoxic CD8+ Temra cells show loss of chromatin accessibility at genes associated with T cell activation
Broader profiling across all memory T cell subsets confirmed that the transcriptional differences between TEMRA and other subsets are tightly coordinated with changes in chromatin accessibility. CD8+ effector memory and TEMRA cells clustered closely together and were the most distinct from naïve cells, with the magnitude of gene expression changes increasing alongside the magnitude of chromatin changes in a correlated fashion.25Communications Biology. Distinct transcriptomic and epigenomic modalities underpin human memory T cell subsets and their activation potential In practical terms, TEMRA cells are not just expressing different genes; their DNA is physically remodeled to make certain activation programs inaccessible. That remodeling may explain why attempts to revert TEMRA cells to a more functional memory state have proven difficult.
Transplant Outcomes and Tissue Infiltration
The transplant setting offers some of the clearest evidence that TEMRA cells matter clinically. In kidney transplant recipients, expansion of TEMRA CD8+ T cells was associated with accumulation of cytolytic T cells in kidney graft biopsies during episodes of humoral rejection. These TEMRA cells showed heightened adhesion to activated endothelium and enhanced transmigration toward chemokine signals, meaning they were not just circulating but actively invading the transplanted organ.5PubMed Central. Effector Memory–Expressing CD45RA (TEMRA) CD8+ T Cells from Kidney Transplant Recipients Exhibit Enhanced Purinergic P2X4 Receptor–Dependent Proinflammatory and Migratory Responses Separately, a restriction of T cell receptor diversity combined with TEMRA expansion was proposed as a potential marker for late graft dysfunction in clinically stable patients, meaning trouble might be brewing even when standard clinical measures look fine.1PubMed Central. Expansion of highly differentiated cytotoxic terminally differentiated effector memory CD8+ T cells in a subset of clinically stable kidney transplant recipients: a potential marker for late graft dysfunction
The relationship between CMV and transplant outcomes adds another layer. CMV reactivation is common after transplantation because immunosuppressive drugs loosen the immune system’s grip on latent viruses. The resulting TEMRA expansion is a double-edged sword: those CMV-specific TEMRA cells help control the virus, but their inflammatory and cytotoxic potential can simultaneously threaten the graft. Balancing viral control against graft protection remains one of the central challenges in transplant immunology, and TEMRA cells sit squarely at the center of that tension.
Why TEMRA Cells Resist Easy Classification
One of the frustrating but genuinely interesting things about TEMRA cells is that they defy the neat categories immunologists would like to put them in. They are called “terminally differentiated,” yet some of them clearly proliferate. They express a naïve cell marker (CD45RA), yet they are among the most experienced cells in the immune system. They carry potent killing molecules, yet in tumors they can become functionally impotent. They accumulate with age and are linked to worse vaccine responses, yet a particular TEMRA-like population predicts better survival in colorectal cancer.
The resolution to most of these contradictions is that “TEMRA” is an umbrella term defined by a handful of surface markers, and the cells underneath that umbrella are more diverse than the label suggests. A CD8+ TEMRA cell expanded by decades of CMV surveillance in a 75-year-old is a different animal from a CD8+ TEMRA cell generated inside a tumor’s hostile microenvironment, even though both wear the same molecular jersey. As single-cell technologies make it possible to look at these cells individually rather than in bulk, the field is steadily carving what was once a single box into multiple functionally distinct subsets. The surface markers that define TEMRA cells remain useful as a starting point, but the biology underneath is proving richer and stranger than the naming convention ever anticipated.