Tumour-infiltrating Leukocytes Research Articles

Activatable near-infrared probes for the detection of specific populations of tumour-infiltrating leukocytes in vivo and in urine.

Tracking the immune microenvironment of tumours is essential for understanding the mechanisms behind the effectiveness of cancer immunotherapies. Molecular imaging of tumour-infiltrating leukocytes (TILs) can be used to non-invasively monitor the tumour immune microenvironment, but current imaging agents do not distinguish TILs from leukocytes resident in other tissues. Here we report a library of activatable molecular probes for the imaging, via near-infrared fluorescence, of specific TILs (including M1 macrophages, cytotoxic T lymphocytes and neutrophils) in vivo in real time and also via excreted urine, owing to the probes' renal clearance. The fluorescence of the probes is activated only in the presence of both tumour and leukocyte biomarkers, which allows for the imaging of populations of specific TILs in mouse models of cancers with sensitivities and specificities similar to those achieved via flow-cytometric analyses of biopsied tumour tissues. We also show that the probes enable the non-invasive evaluation of the immunogenicity of different tumours, the dynamic monitoring of responses to immunotherapies and the accurate prediction of tumour growth under various treatments.

Characterization of the immune cell landscape in CRC: Clinical implications of tumour-infiltrating leukocytes in early- and late-stage CRC.

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths globally. Tumour-infiltrating leukocytes play an important role in cancers, including CRC. We therefore sought to characterize the impact of tumour-infiltrating leukocytes on CRC prognosis. To determine whether the immune cell profile within CRC tissue could influence prognosis, we employed three computational methodologies (CIBERSORT, xCell and MCPcounter) to predict abundance of immune cell types, based on gene expression. This was done using two patient cohorts, TCGA and BC Cancer Personalized OncoGenomics (POG). We observed significant differences in immune cell composition between CRC and normal adjacent colon tissue, as well as differences in based on method of analysis. Evaluation of survival based on immune cell types revealed dendritic cells as a positive prognostic marker, consistently across methodologies. Mast cells were also found to be a positive prognostic marker, but in a stage-dependent manner. Unsupervised cluster analysis demonstrated that significant differences in immune cell composition has a more pronounced effect on prognosis in early-stage CRC, compared to late-stage CRC. This analysis revealed a distinct group of individuals with early-stage CRC which have an immune infiltration signature that indicates better survival probability. Taken together, characterization of the immune landscape in CRC has provided a powerful tool to assess prognosis. We anticipate that further characterization of the immune landscape will facilitate use of immunotherapies in CRC.

Nociceptor neurons affect cancer immunosurveillance

Solid tumours are innervated by nerve fibres that arise from the autonomic and sensory peripheral nervous systems1–5. Whether the neo-innervation of tumours by pain-initiating sensory neurons affects cancer immunosurveillance remains unclear. Here we show that melanoma cells interact with nociceptor neurons, leading to increases in their neurite outgrowth, responsiveness to noxious ligands and neuropeptide release. Calcitonin gene-related peptide (CGRP)—one such nociceptor-produced neuropeptide—directly increases the exhaustion of cytotoxic CD8+ T cells, which limits their capacity to eliminate melanoma. Genetic ablation of the TRPV1 lineage, local pharmacological silencing of nociceptors and antagonism of the CGRP receptor RAMP1 all reduced the exhaustion of tumour-infiltrating leukocytes and decreased the growth of tumours, nearly tripling the survival rate of mice that were inoculated with B16F10 melanoma cells. Conversely, CD8+ T cell exhaustion was rescued in sensory-neuron-depleted mice that were treated with local recombinant CGRP. As compared with wild-type CD8+ T cells, Ramp1−/− CD8+ T cells were protected against exhaustion when co-transplanted into tumour-bearing Rag1-deficient mice. Single-cell RNA sequencing of biopsies from patients with melanoma revealed that intratumoral RAMP1-expressing CD8+ T cells were more exhausted than their RAMP1-negative counterparts, whereas overexpression of RAMP1 correlated with a poorer clinical prognosis. Overall, our results suggest that reducing the release of CGRP from tumour-innervating nociceptors could be a strategy to improve anti-tumour immunity by eliminating the immunomodulatory effects of CGRP on cytotoxic CD8+ T cells.

MTAP deficiency contributes to immune landscape remodelling and tumour evasion.

Methylthioadenosine phosphorylase (MTAP) deficiency occurs in various malignancies and is associated with poor survival in cancer patients. However, the mechanisms underlying tumour progression due to MTAP loss are yet to be elucidated. Utilizing integrated analyses of the transcriptome, proteome and secretome, we demonstrated that MTAP deficiency alters tumour-intrinsic, immune-related pathways and reprograms cytokine profiles towards a tumour-favourable environment. Additionally, MTAP-knockout cells exhibited a marked increase in the immune checkpoint protein PD-L1. Upon co-culturing primary T cells with cancer cells, MTAP loss-mediated PD-L1 upregulation inhibited T cell-mediated killing activity and induced several T cell exhaustion markers. In two xenograft tumour models, we showed a modest increase in average volume of tumours derived from MTAP-deficient cells than that of MTAP-proficient tumours. Surprisingly, a remarkable increase in tumour size was observed in humanized mice bearing MTAP-deficient tumours, as compared to their MTAP-expressing counterparts. Following immunophenotypic characterization of tumour-infiltrating leukocytes by mass cytometry analysis, MTAP-deficient tumours were found to display decreased immune infiltrates with lower proportions of both T lymphocytes and natural killer cells and higher proportions of immunosuppressive cells as compared to MTAP-expressing tumour xenografts. Taken together, our results suggest that MTAP deficiency restructures the tumour immune microenvironment, promoting tumour progression and immune evasion.

Abstract 391: Lrg1 blockade modulates the tumor immune microenvironment and improves the efficacy of cancer therapeutics

Abstract Although the use of checkpoint inhibitors and adoptive T cell therapy have been reported in multiple cancers resulting in a plethora of clinical trials, the efficacy of these therapeutic strategies is often limited by the presence of impaired vasculature in the tumour mass. Indeed, in solid tumors, blood vessels are dysfunctional, leaky and poorly perfused, and thwart not only the efficacy of systemically derived drugs but also the extravasation of T cells, promoting an immunosuppressive microenvironment. Leucine-rich alpha-2-glycoprotein 1 (LRG1) is a secreted glycoprotein that is associated with pathogenic neovascularization, autoimmune diseases, chronic inflammation, and is significantly up-regulated in many solid cancers. We have observed that treatment with a LRG1 function-blocking antibody (15C4) significantly limits growth of solid tumors inducing vessel normalization and functionality. In the present study, we aim to investigate if LRG1 blockade enhances an immunostimulatory milieu, making tumors more responsive to current immunotherapies. Murine melanoma cells harbouring the internal influenza nucleoprotein antigen, NP68, were grafted subcutaneously before antigen-specific F5B6 CD8+ T cells were also transferred. Interestingly, the combination with 15C4 promoted a greater reduction in tumor growth rate. Moreover, not only was the number of donor CD8+ T cells significantly higher when delivered with 15C4, but also the total number of CD3+ T cells was increased following combination therapy, suggesting a more robust host-derived lymphocyte trafficking. As blocking LRG1 normalizes the tumor vasculature and enhances T cell extravasation, we then evaluated whether 15C4 could improve delivery and efficacy of an anti-PD1 checkpoint inhibitor. As monotherapies, both 15C4 and anti-PD1 antibodies induced a marked reduction in tumor volume but when the two were combined, a significant additive effect was also observed. Histological analysis revealed that the combination therapy was associated with a significantly higher number of activated CD8+ T cells, together with enhanced expression of Granzyme B. Current studies are investigating whether the observed boost in cytotoxic T cell density and functionality is a direct consequence of vessel normalization or whether LRG1 blockade is able to modulate the tumour immune microenvironment at different levels: for example, FACS analysis of tumour-infiltrating leukocytes revealed a reduction in the percentage of regulatory T cells after dual therapy, while histological analysis suggested an increase in the number of M1 macrophages. These data show that LRG1 blockade orchestrates a shift in the tumour microenvironment from being immune silent to immune active and, therefore, might represent a novel tool to enhance the efficacy of cancer therapies. Citation Format: Carlotta Camilli, Camilla Pilotti, Marie N. O'Connor, David Kallenberg, Markella Alatsatianos, Angharad H. Watson, Julia Ohme, Athina Dritsoula, Ann Ager, Stephen E. Moss, John Greenwood. Lrg1 blockade modulates the tumor immune microenvironment and improves the efficacy of cancer therapeutics [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 391.

Dexamethasone differentially depletes tumour and peripheral blood lymphocytes and can impact the efficacy of chemotherapy/checkpoint blockade combination treatment

ABSTRACTDexamethasone is a synthetic glucocorticoid commonly used for the prevention and management of side effects in cancer patients undergoing chemotherapy. While it is effective as an anti-emetic and in preventing hypersensitivity reactions, dexamethasone depletes peripheral blood lymphocytes and impacts immune responses. The effect of dexamethasone on the number and quality of tumour-infiltrating leukocytes has not been reported. To address this, we calibrated the dose in two different strains of mice to achieve the same extent of peripheral blood lymphocyte depletion observed in patients with cancer. Doses that caused analogous depletion of T and B lymphocytes and NK cells from the peripheral blood, elicited no change in these populations within the tumour. The expression of immune checkpoint molecules PD-1, OX40, GITR and TIM3 on tumour-infiltrating lymphocytes was not altered. We found that dexamethasone had a small but significant deleterious impact on weakly efficacious chemoimmunotherapy but had no effect when the protocol was highly efficacious. Based on these results, we predict that dexamethasone will have a modest negative influence on the overall effectiveness of chemoimmunotherapy treatment.

Abstract GS1-01: Landscape of the breast tumour microenvironment at single-cell resolution

Abstract Breast cancers are a complex 'ecosystem' of diverse cell types, whose heterotypic interactions play central roles in defining the aetiology of disease and its response to therapy. The next generation of therapies will likely be based upon an integrated understanding of the malignant, microenvironmental and immune states that define the tumour and inform treatment response. However, our poor understanding of the tumour microenvironment (TME) of breast cancers has limited the development and implementation of new drugs that target stromal and immune cells. Single cell genomics (SCG) is a remarkable new platform to examine the compositional, gene expression and other parameters of thousands of cells, rapidly and at scale. We have used a multi-dimensional SCG approach to characterise the TME in a unique cohort of early and metastatic breast cancers with rich clinico-pathological annotation. We have conducted single cell RNA-Sequencing on more than 125,000 cells collected from 22 patients. Malignant cells showed remarkable intra-tumoural heterogeneity for canonical breast cancer features, such as intrinsic subtype, hormone receptor expression and activity, drug targets, drug resistance signatures and transcriptional drivers. Cancer Associated Fibroblasts (CAFs), which are classically studied as a single cell type, were heterogeneous across primary and metastatic sites. Interestingly we identified a myofibroblast-like subset and an inflammatory-mediator subset and propose multi-faceted roles in regulating malignancy and tumour immunity. Distinct transcription factor networks regulated these polarised states. We applied a new method known as CITE-Seq to measure cell surface immune markers and checkpoint proteins simultaneous to RNA-Sequencing. We resolve the tumour-immune milieu with high precision and generate new transcriptional signatures of breast tumour-infiltrating leukocytes. To track lymphocyte clonal dynamics through space and time, we developed a novel method known as RAGE-Seq to permit simultaneous full length lymphocyte receptor- and RNA-sequencing at single cell resolution. We observe clonal expansion and trafficking of CD4+ and CD8+ T lymphocytes between the lymph nodes, blood and tumor of patients. In comparison, B cells were polyclonal, suggesting an absence of antigen-dependent clonal expansion. This data provides by far the most extensive insights into the cellular landscape of breast cancer and will reveal new biomarkers and opportunities for stromal- and immune-based therapy. Citation Format: Swarbrick A, Wu SZ, Roden D, Al-Eryani G, O'Toole S, Lim E. Landscape of the breast tumour microenvironment at single-cell resolution [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS1-01.

PO-390 A workflow for optimised isolation and analysis of tumour infiltrating immune subpopulations

IntroductionSyngeneic mouse tumour models are widely used to analyse tumour immunology due to their fully competent immune-repertoire and have paved the way for novel immunotherapy agents in multiple tumour entities. However, the amount and composition of tumour infiltrating leukocytes (TIL) is highly variable. This complicates targeted analysis, in particular for small leukocyte subpopulations that may not be analysed properly or lost in the background noise. When working with large cohort sizes, immune-phenotyping by flow cytometry is time consuming and highly work intensive. We have developed improved workflows combining automated tissue dissociation with novel TIL specific isolation reagents to allow for more accurate and faster analysis of TILs and TIL subpopulations.Material and methodsWe have developed novel TIL specific enrichment reagents for the magnetic cell sorting (MACS) based isolation directly from dissociated tumour tissue. The composition of these populations before and after separation was analysed by flow cytometry. The developed tools were combined with optimised tissue dissociation and flow panels to establish comprehensive workflows.Results and discussionsWe have established workflows combining optimised and automated tissue dissociation using the gentleMACS platform with TIL specific isolation to improve and accelerate downstream analysis. Isolation of TIL was improved by developing new CD45, CD4+, CD8+, and pan T cell enrichment reagents for MACS-based isolation directly from dissociated tumour tissue. Applying this workflow, CD45 +TIL were enriched to purities above 80%–90% with high yields (>70%) from divers syngeneic mouse tumours. This allowed for rapid and reliable analysis even of small TIL subpopulations. Moreover, by using the newly developed T cell reagents, T cells were enriched to purities higher than 90%, allowing for a reliable analysis of rare T cell subpopulations.Importantly, while TIL or T cell enrichment significantly reduced analysis time and reagent costs in immune subset analysis, the composition of infiltrating cells was not affected, excluding the risk of introducing a bias by this method.ConclusionWe have developed improved workflows for the isolation of generic TIL and T cells from mouse tumours reducing time and costs of downstream analysis while standardising and enhancing the detection and quantification of immune cell subpopulations. CD45 +TILs, pan-, CD4+- or CD8+-T cells can directly be isolated from dissociated mouse tumours and analysed for subpopulations.

Peripheral T cell responses to tumour antigens are associated with molecular, immunogenetic and cellular features of breast cancer patients.

Breast cancer is a leading cause of cancer deaths in women, but despite steady improvements in therapies, treatment is still suboptimal. Immunotherapy holds promise as a more effective therapy for breast cancer; supporting this, our prior study showed that patients possessing HER2-reactive CD8+T cells in blood experience survival superior to patients without these cells. Here, we define a composite set of biomarkers that identify patients with T cell responses to tumour antigens. We assessed T cell responses following in vitro stimulation with the HER2, MUC1 and SUR tumour-associated antigens (TAA) by flow cytometry and intracellular cytokine staining in 50 breast cancer patients. We also measured HLA type, serum cytokines, tumour-infiltrating leukocytes and blood leukocyte populations. We found few correlations between TAA-reactive T cells and HLA type, serum cytokines and tumour-infiltrating leukocytes, whereas blood leukocyte phenotypes broadly correlated with TAA responses. This showed monocytes, natural killer cells, dendritic cells and T cells to be inversely associated with both CD4+and CD8+T cells reactive to tumour antigens. Moreover, combining multiple parameters improved the accuracy in predicting patients with TAA-responsive T cells. This study therefore defines composite immune profiles that identify patients responding to TAAs which may allow better personalisation of cancer therapies.

ALK-rearranged adenocarcinoma with extensive mucin production can mimic mucinous adenocarcinoma: clinicopathological analysis and comprehensive histological comparison with KRAS-mutated mucinous adenocarcinoma

We aimed to investigate clinicopathological features and histology of ALK-rearranged adenocarcinomas with extensive mucin production (AEM) that mimic mucinous adenocarcinoma (MA). Retrospectively, 12 cases of AEM and 25 cases of MA harbouring KRAS mutation were retrieved. The clinicopathological profile and detailed histological features were analysed and compared based on the ALK and KRAS status. AEMs occurred in younger patients (p= 0.044) and were characterised by floating tubulopapillary pattern (p < 0.001), prominent nucleolus (p < 0.001), and apical cytoplasmic snouts (p < 0.001). In contrast, KRAS-mutated MAs lacked ALK-specific histological patterns (p < 0.05). Instead, tumour-infiltrating leukocytes (p= 0.018) and smooth cytoplasmic borders (p < 0.001) with vesicular nuclei (p= 0.004) were prominent in KRAS-mutated MAs. AEMs demonstrated characteristic tubulopapillary pattern and apical snouts, which were distinguishing features from MAs with KRAS mutation. Apical snouts can be a useful histological surrogate for ALK rearrangement in the pulmonary adenocarcinomas showing extensive mucin that mimic MA.

Immunological hallmarks of stromal cells in the tumour microenvironment

A dynamic and mutualistic interaction between tumour cells and the surrounding stroma promotes the initiation, progression, metastasis and chemoresistance of solid tumours. Far less understood is the relationship between the stroma and tumour-infiltrating leukocytes; however, emerging evidence suggests that the stromal compartment can shape antitumour immunity and responsiveness to immunotherapy. Thus, there is growing interest in elucidating the immunomodulatory roles of the stroma that evolve within the tumour microenvironment. In this Review, we discuss the evidence that stromal determinants interact with leukocytes and influence antitumour immunity, with emphasis on the immunological attributes of stromal cells that may foster their protumorigenic function.

Inflammatory tumour microenvironment is associated with superior survival in hepatocellular carcinoma patients

Hepatocellular carcinoma (HCC) is an aggressive malignancy with few treatment options. As the status of the tumour immune microenvironment can affect progression of established tumours, we evaluated potential immune mechanisms associated with survival in HCC. Immune gene expression profiles were analyzed in tumour and non-tumour liver tissues from resected HCC patients using quantitative PCR and immunohistochemistry. Tumour-infiltrating leukocytes (TILs) were isolated to verify the expression of immune genes and to identify proliferating TILs. These parameters were analyzed statistically in relation with patient survival and tumour phenotype (apoptosis and proliferation). The immune microenvironment within tumours was found to be heterogeneous, although globally more inert compared to the adjacent non-tumour liver tissue. Univariate analysis in 61 patients identified a group of innate immune genes whose expression within tumours is positively associated with patient survival. TNF, IL6 and CCL2 are the most significant genes, with TNF being an independent predictor of survival in multivariate analysis. The gene set includes macrophage and NK-associated molecules such as TLR4, TLR3, CCR2, NCR3. Most of these molecules are expressed by TILs. Importantly, proliferating immune cells, predominantly NK and T cells, are present in tumours of patients with longer survival, and exclusively in areas devoid of proliferating tumour cells. NK and CD8(+) T cell densities are correlated positively with tumour apoptosis, and negatively with tumour proliferation. Hence, an inflammatory immune microenvironment within HCC tumours could be an important means to control tumour progression via TIL activation and proliferation.

Search for effective therapy against glioblastoma multiforme—clinical immunisation with autologous glioma cells transduced with the human interferon-γ gene

Based upon earlier experimental work by our group, we have started a human immuno-gene therapy study. The goal is to study the effects of immunisation with autologous tumour cells expressing gene sequences for human interferon-γ. For more than two decades we have sought for efficient treatment against malignant gliomas. Our most successful treatment in the animal models is immuno-gene therapy where murine genes for the cytokines IFN-γ, IL-7 and B7-1 were chosen for their ability to stimulate different stages of the pathway for cytotoxic T lymphocyte (CTL) activation. Rats of the syngeneic inbred strain Fischer 344 had rat glioma cells of the N32 line inoculated in the right caudate nucleus, and 1 or 3 days later N32 cells transfected with either IFN-γ, IL-7 or B7-1 genes were injected subcutaneously (and in some studies intraperitoneally). This treatment was repeated three to four times with 7- to 14-day interval and resulted in significantly improved survival compared with treatment with wild-type rat glioma cells (e.g. not transfected with the cytokine genes). The continued work concentrated on treatment with IFN-γ secreting tumour cells of both the N32 line and also a newly developed ENU-induced rat glioma cell line called N29. This work proved the effectiveness of the technique. Cure was achieved in 72% of the animals treated with the IFN-γ cells. Tumour-infiltrating leukocytes from N32-IFN-γ-immunised animals showed a significantly stronger infiltration by CD 8+ T-cells, significantly more NK cells, and an increased number of CD25-expressing T-cells. These results confirmed the possible usefulness of IFN-γ-transfected tumour cells in the immune-therapy of rat brain tumours. The animal experiments have motivated us to start a human immuno-gene therapy study including 20 patients with glioblastoma multiforme (GBM), where >80% of the tumour can be surgically removed. The goal is to ascertain whether immunisation with autologous tumour cells expressing gene sequences for human interferon-γ is safe for the patients, gives rise to an immunological response, and adds any beneficial effect to conventional therapy (tumour growth, prolonged survival). Hitherto, nine patients have been included in the study, two of which have received 6 and 10 immunisations, respectively. Two patients have died from their disease before cells have been ready for immunisation; in two cases no malignant cells have appeared in the cell cultures and three patients are ready to start their immunisation shortly. The immunisation takes place in the dermis of the upper arm. Seven days after each immunisation, a skin biopsy is taken from the centre of one of the injection sites. The composition of the cellular infiltration in the skin is studied by markers for T lymphocytes (CD3); helper cells, subset of T cells (CD4); killer cells, subset of T cells (CD8); natural killer cells (CD16) and B lymphocytes, B cells (CD20). Also the expression of cytokines for functional T cell subsets are studied: IL-2, IL-4, IL-10, IL-12, IL-18, TNF-α and IF-γ and TGF-β 1,2 and 3. Peripheral blood is sampled both before and after operation and also after each immunisation event. Co-culture of this blood with tumour cells from the patient allows for a selection of T-cells that can recognise tumour-specific antigens. The results from the first human treatments are presented.

Little expression of cytokine mRNA by fresh tumour-infiltrating mononuclear leukocytes from glioma and lung adenocarcinoma.

We investigated whether cytokine genes were activated in human tumour-infiltrating mononuclear leukocytes (TIML) obtained from six lung adenocarcinomas and seven glioblastomas. TIML were extracted by mechanical disruption and isolated by double density gradient of Ficoll. We performed mRNA reverse transcription-polymerase chain reaction (RT-PCR) on these fresh (noncultured) TIML and autologous peripheral blood mononuclear leukocytes (PBML) using primers for the cytokines IL-1 beta, IL-6, IL-2, IL-4, GM-CSF, IFN-gamma and TNF-beta. In addition, we compared patients' TIML and PBML populations with healthy normal and alpha-CD3 activated PBML as an optimally activated reference population. Gel bands of RT-PCR products were quantitated in relative units (RU) as a function of their size and intensity by computerized image-analysis. Lung and brain patients' TIML showed IL-1 beta and IL-6 cytokine mRNA expressed in the average of 2-log RU but not significantly different from autologous and normal healthy PBML. IL-2, IFN-gamma and TNF-beta also did not appear expressed in the TIML at higher levels than in autologous or healthy normal PBML. However in two thirds of patients, lung TIML could be distinguished from autologous PBML by specific expression of GM-CSF and from healthy normal PBML by expression of IL-4. Similarly, most brain TIML expressed mRNA significantly above healthy normal PBML for GM-CSF and IL-4. In comparison with alpha-CD3 activated healthy PBML, our results suggest that lung and brain TIML had detectable cytokine mRNA, but they seemed poorly activated in total number of genes and amount of cytokine mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of cytotoxic effector cell activity in colon 38 tumours following treatment with flavone acetic acid

Host cells have been implicated as being involved in the antitumour effects of flavone acetic acid (FAA), an agent with selectivity towards solid tumours which is currently undergoing clinical trial. To determine whether tumour-associated host cells are affected by FAA treatment, tumour-infiltrating leukocytes (TIL) were isolated from subcutaneous Colon 38 tumours, which are known to be sensitive to FAA. 1–2 × 10 5 TIL were isolated per gram of tumour, comprising mainly small lymphocytes and macrophages. Spontaneous activity against YAC- 1 and P 815 tumour targets was tested in a 4 h 51Cr -release assay for lymphoid cytotoxic effector cells. High levels of activity were exhibited by TIL against both P 815, which is resistant to natural killer (NK) cells, and to NK-sensitive YAC- 1 cells. In contrast, splenic cell populations contained only NK cell activity. Within 1 h of intraperitoneal administration of FAA ( 330 mg/kg) the cytotoxic effector cell activity of the TIL population was dramatically depressed, remaining low during the time in which extensive tumour necrosis became evident. In contrast, splenic NK activity was unchanged at 1 h and elevated at 4 h. The decrease in lymphoid killer activity of the TIL population following treatment argues against the primary involvement of these effector cells in mediating the antitumour action of FAA.