scholarly journals 157 Lymph node targeted boosting with cognate amphiphile-peptide vaccines enhances TCR-T Cell therapy to eradicate solid tumors

2021 ◽  
Vol 9 (Suppl 3) ◽  
pp. A167-A167
Author(s):  
Dylan Drakes ◽  
Abdulraouf Abbas ◽  
Jacqueline Shields ◽  
Peter DeMuth

BackgroundClinical results from TCR-T Cell therapies demonstrate anti-tumor efficacy, although therapeutic benefits remain transient due to suboptimal T Cell functional persistence and tumor infiltration alongside antigen escape mechanisms.1 2 3 4 5 Amphiphile (AMP) vaccines improve lymph node targeting of cancer immunogens, stimulating an enhanced endogenous anti-tumor response.6 7 We describe an approach to generate robust and durable anti-tumor responses by combining AMP lymphatic targeting with TCR-T Cell therapy. AMP cognate peptides traffic to lymph nodes and improve TCR-T Cell activation, persistence, and function compared to soluble (SOL) peptide vaccination or TCR-T Cells alone, inducing a superior anti-tumor effect.MethodsC57BL/6J mice were subcutaneously implanted with B16F10 10 days prior to transduced pmel-1 T cell transfer or 75 days after T cell treatment for rechallenge experiments. Tumor-bearing mice received 5 doses, 2x/week of AMP-GP100/AMP-CpG, SOL-GP100/SOL-CpG, or PBS by tail-base vaccination. Caliper measurements determined tumor progression and overall survival. TCR-T Cell persistence was assessed bi-weekly through retro-orbital bleeds. Tumors and lymph nodes from treated mice were excised and analyzed by Nanostring for differential gene expression and flow cytometry for TCR-T Cell functional persistence and T cell epitope spread. Human T Cells (HTCs) and Dendritic Cells (DCs) were isolated from autologous PBMCs, transduced with KRAS-specific TCRs, and cultured with AMP-KRAS-peptide pulsed DCs before assaying T Cell boosting.ResultsWe demonstrate that AMP vaccination expands tumor specific TCR-T Cells in vivo up to 46-fold while enhancing the activation, cytokine secretion, and pro-inflammatory gene expression of tumor-infiltrating TCR-T Cells. Endogenous tumor-infiltrating T cells from AMP vaccinated mice produced up to 17-fold greater cytokine secretion following re-stimulation with non-targeted tumor epitopes. These results correspond to the eradication of established B16F10 tumors and a resistance to secondary tumor challenge in cured mice. Providing clinical relevance, HTCs transduced with KRAS-specific TCRs and boosted with AMP-KRAS-peptide pulsed DCs exhibited enhanced T cell activation, Th1 cytokine secretion, and cytolytic capacity compared to HTCs exposed to unlabeled DCs.ConclusionsAMP vaccination delivers cognate peptides to lymph nodes providing in vivo activation of tumor-specific TCR-T Cells which amplifies anti-tumor potency of such adoptively transferred cells. AMP vaccination significantly enhanced TCR-T Cell anti-tumor response and led to durable cures of solid tumors in an established, syngeneic tumor model. Additionally, AMP-peptide pulsed autologous DCs enhanced the function of clinically relevant KRAS-specific TCR-T cells in vitro. Taken together, these studies provide direct rationale and evidence for the combination of AMP vaccination with TCR-T Cell therapies to augment clinical responses.ReferencesRobbins PF, Morgan RA, Feldman SA, Yang JC, Sherry RM, Dudley ME, Wunderlich JR, Nahvi AV, Helman LJ, Mackall CL, et al. Tumor regression in patients with metastatic synovial cell sarcoma and melanoma using genetically engineered lymphocytes reactive with NY-ESO-1. J Clin Oncol 2011;29:917–924. doi: 10.1200/JCO.2010.32.2537.Rapoport AP, Stadtmauer EA, Binder-Scholl GK, Goloubeva O, Vogl DT, Lacey SF, Badros AZ, Garfall A, Weiss B, Finklestein J, et al. NY-ESO-1-specific TCR-engineered T cells mediate sustained antigen-specific antitumor effects in myeloma. Nat Med 2015;21:914–921. doi: 10.1038/nm.3910.Doran SL, Stevanovic S, Adhikary S, Gartner JJ, Jia L, Kwong MLM, Faquin WC, Hewitt SM, Sherry RM, Yang JC, et al. T-Cell Receptor Gene Therapy for Human Papillomavirus-Associated Epithelial Cancers: A First-in-Human, Phase I/II Study. J Clin Oncol 2019;37:2759–2768. doi: 10.1200/JCO.18.02424.Chandran SS, Klebanoff CA. T cell receptor-based cancer immunotherapy: Emerging efficacy and pathways of resistance. Immunol Rev 2019;290:127–147. doi: 10.1111/imr.12772.D’Angelo SP, Melchiori L, Merchant MS, Bernstein D, Glod J, Kaplan R, Grupp S, Tap WD, Chagin K, Binder GK, et al. Antitumor Activity Associated with Prolonged Persistence of Adoptively Transferred NY-ESO-1 (c259)T Cells in Synovial Sarcoma. Cancer Discov 2018;8:944–957. doi: 10.1158/2159-8290.CD-17-1417.H Liu, KD Moynihan, Y Zheng, GL Szeto, AV Li, B Huang, DS Van Egeren, C Park, DJ Irvine. Structure-based programming of lymph-node targeting in molecular vaccines. Nature 2014;507: 519–522. doi: 10.1038/nature12978.KD Moynihan, CF Opel, GL Szeto, A Tzeng, EF Zhu, JM Engreitz, RT Williams, K Rakhra, MH Zhang, AM Rothschilds, S Kumari, RL Kelly, BH Kwan, W Abraham, K Hu, NK Mehta, MJ Kauke, H Suh, JR Cochran, DA Lauffenburger, KD Wittrup, DJ Irvine. Eradication of large established tumors in mice by combination immunotherapy that engages innate and adaptive immune responses. Nat Med 2016; 22: 1402–1410. doi: 10.1038/nm.4200.

2016 ◽  
Vol 113 (26) ◽  
pp. 7201-7206 ◽  
Author(s):  
Ying S. Hu ◽  
Hu Cang ◽  
Björn F. Lillemeier

T cells become activated when T-cell receptors (TCRs) recognize agonist peptides bound to major histocompatibility complex molecules on antigen-presenting cells. T-cell activation critically relies on the spatiotemporal arrangements of TCRs on the plasma membrane. However, the molecular organizations of TCRs on lymph node-resident T cells have not yet been determined, owing to the diffraction limit of light. Here we visualized nanometer- and micrometer-scale TCR distributions in lymph nodes by light sheet direct stochastic optical reconstruction microscopy (dSTORM) and structured illumination microscopy (SIM). This dSTORM and SIM approach provides the first evidence, to our knowledge, of multiscale reorganization of TCRs during in vivo immune responses. We observed nanometer-scale plasma membrane domains, known as protein islands, on naïve T cells. These protein islands were enriched within micrometer-sized surface areas that we call territories. In vivo T-cell activation caused the TCR territories to contract, leading to the coalescence of protein islands and formation of stable TCR microclusters.


1997 ◽  
Vol 185 (12) ◽  
pp. 2133-2141 ◽  
Author(s):  
Elizabeth Ingulli ◽  
Anna Mondino ◽  
Alexander Khoruts ◽  
Marc K. Jenkins

Although lymphoid dendritic cells (DC) are thought to play an essential role in T cell activation, the initial physical interaction between antigen-bearing DC and antigen-specific T cells has never been directly observed in vivo under conditions where the specificity of the responding T cells for the relevant antigen could be unambiguously assessed. We used confocal microscopy to track the in vivo location of fluorescent dye-labeled DC and naive TCR transgenic CD4+ T cells specific for an OVA peptide–I-Ad complex after adoptive transfer into syngeneic recipients. DC that were not exposed to the OVA peptide, homed to the paracortical regions of the lymph nodes but did not interact with the OVA peptide-specific T cells. In contrast, the OVA peptide-specific T cells formed large clusters around paracortical DC that were pulsed in vitro with the OVA peptide before injection. Interactions were also observed between paracortical DC of the recipient and OVA peptide-specific T cells after administration of intact OVA. Injection of OVA peptide-pulsed DC caused the specific T cells to produce IL-2 in vivo, proliferate, and differentiate into effector cells capable of causing a delayed-type hypersensitivity reaction. Surprisingly, by 48 h after injection, OVA peptide-pulsed, but not unpulsed DC disappeared from the lymph nodes of mice that contained the transferred TCR transgenic population. These results demonstrate that antigen-bearing DC directly interact with naive antigen-specific T cells within the T cell–rich regions of lymph nodes. This interaction results in T cell activation and disappearance of the DC.


2003 ◽  
Vol 198 (5) ◽  
pp. 715-724 ◽  
Author(s):  
Marc Bajénoff ◽  
Samuel Granjeaud ◽  
Sylvie Guerder

The development of an immune response critically relies on the encounter of rare antigen (Ag)-specific T cells with dendritic cells (DCs) presenting the relevant Ag. How two rare cells find each other in the midst of irrelevant other cells in lymph nodes (LNs) is unknown. Here we show that initial T cell activation clusters are generated near high endothelial venules (HEVs) in the outer paracortex of draining LNs by retention of Ag-specific T cells as they exit from HEVs. We further show that tissue-derived DCs preferentially home in the vicinity of HEVs, thus defining the site of cluster generation. At this location DCs efficiently scan all incoming T cells and selectively retain those specific for the major histocompatibility complex–peptide complexes the DCs present. Such strategic positioning of DCs on the entry route of T cells into the paracortex may foster T cell–DC encounter and thus optimize initial T cell activation in vivo.


Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 1671-1671
Author(s):  
Harbani Malik ◽  
Ben Buelow ◽  
Brian Avanzino ◽  
Aarti Balasubramani ◽  
Andrew Boudreau ◽  
...  

Abstract Introduction Along with CD20 and CD22, the restricted expression of CD19 to the B-cell lineage makes it an attractive target for the therapeutic treatment of B-cell malignancies. Many monoclonal antibodies and antibody drug conjugates specific to CD19 have been described, including bispecific T-cell redirecting antibodies (T-BsAbs). In addition, anti-CD19 chimeric antigen receptor T-cells (CAR-Ts) have been approved to treat leukemia. To date, toxicity from over-activation of T-cells and large-scale production of CAR-Ts still hinder this approach. Bispecific T-cell engaging antibodies redirecting T cells to CD19 circumvent the latter problem but to date have shown similar T-cell over-activation, as well as significant neurotoxicity. Utilizing TeneoSeek, a next generation sequencing (NGS)-based discovery pipeline that uses in silico analysis of heavy chain only/fixed light chain antibody (HCA/Flic, respectively) sequences to enrich for antigen specific antibodies, we made a high affinity αCD19 HCA and a library of αCD3 Flic antibodies that showed a >2 log range of EC50s for T cell activation in vitro. Of note, the library contained a selectively-activating αCD3 that induced potent T-cell dependent lysis of lymphoma cells (when paired with an αCD19 HCA) with minimal cytokine secretion. To characterize the relative efficacy and potential therapeutic window of this unique molecule, we compared the low-activating (and Fc-containing) CD19 x CD3 to two pan T-cell activating bispecific CD19 x CD3 antibodies (blinatumomab and another developed in-house) in vitro and in vivo for T-cell activation, efficacy in killing lymphoma cells, and toxicity. Methods T-cell activation was measured via flow cytometry (CD69 and CD25 expression) and cytokine ELISA (IL-2, IL-6, IL-10, INF-ɣ, and TNFα) in vitro. Lysis of B-cell tumor cell lines (Raji, Ramos, and Nalm6) was measured via calcein release in vitro. In vivo, NOG mice were engrafted with human peripheral blood mononuclear cells (huPBMC) and human lymphoma cell lines, and the mice treated with weekly injections of T-BsAbs. Tumor burden was evaluated via caliper measurement. Pharmacokinetic (PK) studies were performed in NOG mice using ELISA. Results EC50s for cytotoxicity were in the single-digit nanomolar range for the selective T cell activating T-BsAb and sub-nanomolar for the pan T-cell activating controls. The selective T cell activator showed markedly reduced cytokine release for all cytokines tested compared to the pan T-cell controls even at saturating concentrations. In vivo, established CD19 positive B-cell tumors were cleared in NOG mice in the presence of huPBMC. PK profiles of both molecules generated in-house (selective and pan T-cell activators) were consistent with those of an IgG in mice. No activation of T-cells was observed in vitro or in vivo in the absence of CD19 expressing target cells. Conclusions Both the selectively-activating and the pan T-cell activating control bispecific antibodies killed lymphoma cells in vitro and in vivo in a CD19-dependent manner. While the pan T-cell activating controls showed T-cell activation comparable to other CD3-engaging bispecifics, the selective activator induced significantly reduced cytokine secretion by T-cells and demonstrated a half-life consistent with other IgG antibodies. In summary, our selectively activating CD19 x CD3 T-BsAb shows promise as a lymphoma therapeutic differentiated from current T-cell targeted therapies currently in the clinic and in clinical trials. Disclosures Malik: Teneobio, Inc.: Employment. Buelow:Teneobio Inc.: Employment. Avanzino:Teneobio, Inc.: Employment. Balasubramani:Teneobio, Inc.: Employment. Boudreau:Teneobio, Inc.: Employment. Clarke:Teneobio, Inc.: Employment. Dang:Teneobio, Inc.: Employment. Davison:Teneobio, Inc.: Employment. Force Aldred:Teneobio Inc.: Employment. Harris:Teneobio, Inc.: Employment. Jorgensen:Teneobio, Inc.: Employment. Li:Teneobio, Inc.: Employment. Medlari:Teneobio, Inc.: Employment. Narayan:Teneobio, Inc.: Employment. Ogana:Teneobio, Inc.: Employment. Pham:Teneobio Inc.: Employment. Prabhakar:Teneobio, Inc.: Employment. Rangaswamy:Teneobio, Inc.: Employment. Sankaran:Teneobio, Inc.: Employment. Schellenberger:Teneobio, Inc.: Employment. Ugamraj:Teneobio, Inc.: Employment. Trinklein:Teneobio, Inc.: Employment. Van Schooten:Teneobio, Inc.: Employment.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Siao-Yi Wang ◽  
Tamson V. Moore ◽  
Annika V. Dalheim ◽  
Gina M. Scurti ◽  
Michael I. Nishimura

AbstractAdoptive T cell therapy with T cell receptor (TCR)-modified T cells has shown promise in treating metastatic melanoma and other malignancies. However, studies are needed to improve the efficacy and durability of responses of TCR-modified T cells. Standard protocols for generating TCR-modified T cells involve activating T cells through CD3 stimulation to allow for the efficient transfer of tumor-reactive receptors with viral vectors. T cell activation results in terminal differentiation and shortening of telomeres, which are likely suboptimal for therapy. In these studies, we demonstrate efficient T cell transduction with the melanoma-reactive TIL1383I TCR through culturing with interleukin 7 (IL-7) in the absence of CD3 activation. The TIL1383I TCR-modified T cells generated following IL-7 culture were enriched with naïve (TN) and memory stem cell populations (TSCM) while maintaining longer telomere lengths. Furthermore, we demonstrated melanoma-reactivity of TIL1383I TCR-modified cells generated following IL-7 culture using in vitro assays and a superior response in an in vivo melanoma model. These results suggest that utilizing IL-7 to generate TCR-modified T cells in the absence of activation is a feasible strategy to improve adoptive T cell therapies for melanoma and other malignancies.


2008 ◽  
Vol 76 (12) ◽  
pp. 5817-5825 ◽  
Author(s):  
Annalisa Ciabattini ◽  
Elena Pettini ◽  
Peter Andersen ◽  
Gianni Pozzi ◽  
Donata Medaglini

ABSTRACT The primary activation of T-helper and T-cytotoxic cells following mucosal immunization with recombinant Streptococcus gordonii was studied in vivo by adoptive transfer of ovalbumin (OVA)-specific transgenic CD8+ (OT-I) and CD4+ (OT-II) T cells. A recombinant strain, expressing on the surface the vaccine antigen Ag85B-ESAT-6 from Mycobacterium tuberculosis fused to OVA T-helper and T-cytotoxic epitopes (peptides 323 to 339 and 257 to 264), was constructed and used to immunize C57BL/6 mice by the intranasal route. Recombinant, but not wild-type, bacteria induced OVA-specific CD4+ and CD8+ T-cell clonal expansion in cervical lymph nodes, lung, and spleen. OVA-specific CD4+ and CD8+ T-cell proliferation appeared first in cervical lymph nodes and later in the spleen, suggesting a possible migration of activated cells from the inductive site to the systemic district. A significant correlation between the percentages of CD4+ and CD8+ proliferating T cells was observed for each animal. The expression of CD69, CD44, and CD45RB on proliferating T lymphocytes changed as a function of the cell division number, confirming T-cell activation following the antigen encounter. These data indicate that intranasal immunization with recombinant S. gordonii is capable of inducing primary activation of naive antigen-specific CD4+ and CD8+ T cells, both locally and systemically.


2021 ◽  
Author(s):  
Siao-Yi Wang ◽  
Tamson V. Moore ◽  
Annika V. Dalheim ◽  
Gina M. Scurti ◽  
Michael I. Nishimura

Abstract Adoptive T cell therapy with T cell receptor (TCR)-modified T cells has shown promise in treating metastatic melanoma and other malignancies. However, studies are needed to improve the efficacy and durability of responses of TCR-modified T cells. Standard protocols for generating TCR-modified T cells involve activating T cells through CD3 stimulation to allow for the efficient transfer of tumor-reactive receptors with viral vectors. T cell activation results in terminal differentiation and shortening of telomeres, which are likely suboptimal for therapy. In these studies, we demonstrate efficient T cell transduction with the melanoma-reactive TIL1383I TCR through culturing with interleukin 7 (IL-7) in the absence of CD3 activation. The TIL1383I TCR-modified T cells generated following IL-7 culture were enriched with naïve (TN) and memory stem cell populations (TSCM) while maintaining longer telomere lengths. Furthermore, we demonstrated melanoma-reactivity of TIL1383I TCR-modified cells generated following IL-7 culture using in vitro assays and a superior response in an in vivo melanoma model. These results suggest that utilizing IL-7 to generate TCR-modified T cells in the absence of activation is a feasible strategy to improve adoptive T cell therapies for melanoma and other malignancies.


Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 4550-4550 ◽  
Author(s):  
Tsvetelina Pentcheva-Hoang ◽  
David Torres ◽  
Tania Rodriguez ◽  
Ana Korngold ◽  
An Lu ◽  
...  

Abstract Introduction: Use of T cells engineered to express antigen-specific T cell receptors (TCRs) has shown promise as a cancer immunotherapy treatment; however, durable responses have been limited by poor T cell persistence and expansion in vivo. Additionally, MHC class I downregulation on tumor cells further reduces therapeutic efficacy. Therefore, we co-expressed in human T cells a novel, small molecule dimerizer (rimiducid)-dependent T cell "activation switch", called inducible MyD88/CD40 (iMC), along with tumor antigen-specific TCRs to regulate T cell activation and expansion, while upregulating MHC class I expression on tumor cells. Methods: Human T cells were activated with anti-CD3/CD28 and transduced with g-retroviruses encoding TCR α and β chains recognizing either the cancer-testes antigen PRAME (HLA-A*201-restricted SLLQHLIGL) or the B cell-specific transcriptional co-activator, Bob1/OBF-1 (HLA-B*702-restricted APAPTAVVL). Parallel "GoTCR" vectors co-expressed the αβ TCR and iMC, comprising signaling domains from MyD88 and CD40 fused in-frame with tandem rimiducid-binding FKBP12v36 domains. Proliferation, cytokine production and cytotoxicity of modified T cells was assessed using peptide-pulsed EGFPluc-expressing T2 cells (PRAME only) or PRAME+/Bob1+, HLA-A2+ HLA-B7+ EGFPluc-expressing U266 myeloma cells ± rimiducid (10 nM). MHC class I upregulation on tumor cells was measured using transwell assays and flow cytometry. In vitro tumor killing and T cell proliferation were analyzed using T cell and tumor coculture assays by either measuring loss of luciferase activity overnight or by flow cytometry over a period of 4-7 days. Finally, in vivo efficacy was determined using immune-deficient NSG mice engrafted i.v. with U266 cells and treated i.v. with 5x106-1x107 transduced T cells. iMC was activated in vivo by weekly or biweekly i.p. rimiducid injections (1-5 mg/kg). Tumor size and T cell expansion was measured using in vivo bioluminescence imaging and flow cytometry, respectively. Results: All vectors efficiently (~85%) transduced activated T cells and showed antigen-specific IFN-g production and cytolytic function against peptide-pulsed T2 cells and/or PRAME+Bob1+ U266 myeloma cells. However, both TCR ligation and rimiducid-dependent iMC costimulation were required for IL-2 production against PRAME peptide-pulsed T2 cells. Coculture assays against U266 cells showed that tumor elimination was optimized with concurrent rimiducid-driven iMC activation in both "GoPRAME" and "GoBob1" constructs, and this was accompanied by greatly increased IL-2 secretion and robust T cell proliferation (~ 50-fold vs PRAME or Bob1-specific TCRs alone). Further, iMC activation produced IFN-g independently of TCR ligation, which significantly increased MHC class I expression on tumor cells (~ 7-fold) relative to PRAME TCR-transduced T cells. In NSG mice engrafted with PRAME+ U266 myeloma tumors, GoPRAME TCR-modified T cells persisted for at least 81 days post-injection and prevented tumor growth, unlike any of the other T cell groups. Importantly, weekly rimiducid injection dramatically expanded iMC-PRAME TCR-expressing T cell numbers by ~1000-fold on day 81 post-injection compared to T cells expressing only the PRAME TCR (p < 0.001). Summary: iMC is a novel "Go" switch that utilizes rimiducid, a small molecule dimerizer, to provide costimulation to PRAME and Bob1-specific TCR-engineered T cells while sensitizing tumors to TCR-mediated recognition via cytokine-induced MHC I upregulation. These iMC-enhanced TCRs are prototypes of novel "GoTCR" engineered T cell therapies that may increase efficacy, safety and durability of adoptive T cell therapies. Disclosures Pentcheva-Hoang: Bellicum Pharmaceuticals: Employment. Torres:Bellicum Pharmaceuticals: Employment. Rodriguez:Bellicum Pharmaceuticals: Employment. Korngold:Bellicum Pharmaceuticals: Employment. Lu:Bellicum Pharmaceuticals: Employment. Crisostomo:Bellicum Pharmaceuticals: Employment. Moseley:Bellicum Pharmaceuticals: Employment, Membership on an entity's Board of Directors or advisory committees. Slawin:Bellicum Pharmaceuticals: Employment, Equity Ownership. Spencer:Bellicum Pharmaceuticals: Employment, Equity Ownership. Foster:Bellicum Pharmaceuticals: Employment.


2021 ◽  
Vol 118 (34) ◽  
pp. e2106612118
Author(s):  
Linfeng Yang ◽  
Jianli Yin ◽  
Jiali Wu ◽  
Longliang Qiao ◽  
Evan M. Zhao ◽  
...  

Chimeric antigen receptor (CAR)–engineered T cell therapies have been recognized as powerful strategies in cancer immunotherapy; however, the clinical application of CAR-T is currently constrained by severe adverse effects in patients, caused by excessive cytotoxic activity and poor T cell control. Herein, we harnessed a dietary molecule resveratrol (RES)–responsive transactivator and a transrepressor to develop a repressible transgene expression (RESrep) device and an inducible transgene expression (RESind) device, respectively. After optimization, these tools enabled the control of CAR expression and CAR-mediated antitumor function in engineered human cells. We demonstrated that a resveratrol-repressible CAR expression (RESrep-CAR) device can effectively inhibit T cell activation upon resveratrol administration in primary T cells and a xenograft tumor mouse model. Additionally, we exhibit how a resveratrol-inducible CAR expression (RESind-CAR) device can achieve fine-tuned and reversible control over T cell activation via a resveratrol-titratable mechanism. Furthermore, our results revealed that the presence of RES can activate RESind-CAR T cells with strong anticancer cytotoxicity against cells in vitro and in vivo. Our study demonstrates the utility of RESrep and RESind devices as effective tools for transgene expression and illustrates the potential of RESrep-CAR and RESind-CAR devices to enhance patient safety in precision cancer immunotherapies.


1999 ◽  
Vol 189 (3) ◽  
pp. 593-598 ◽  
Author(s):  
Adrian L. Smith ◽  
Barbara Fazekas de St. Groth

Two subsets of murine splenic dendritic cells, derived from distinct precursors, can be distinguished by surface expression of CD8α homodimers. The functions of the two subsets remain controversial, although it has been suggested that the lymphoid-derived (CD8α+) subset induces tolerance, whereas the myeloid-derived (CD8α−) subset has been shown to prime naive T cells and to generate memory responses. To study their capacity to prime or tolerize naive CD4+ T cells in vivo, purified CD8α+ or CD8α− dendritic cells were injected subcutaneously into normal mice. In contrast to CD8α− dendritic cells, the CD8α+ fraction failed to traffic to the draining lymph node and did not generate responses to intravenous peptide. However, after in vitro pulsing with peptide, strong in vivo T cell responses to purified CD8α+ dendritic cells could be detected. Such responses may have been initiated via transfer of peptide–major histocompatibility complex complexes to migratory host CD8α− dendritic cells after injection. These data suggest that correlation of T helper cell type 1 (Th1) and Th2 priming with injection of CD8α+ and CD8α− dendritic cells, respectively, may not result from direct T cell activation by lymphoid versus myeloid dendritic cells, but rather from indirect modification of the response to immunogenic CD8α− dendritic cells by CD8α+ dendritic cells.


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