抗人喉癌/抗VEGF双功能抗体制备及应用研究

目的：研制抗人喉癌／抗血管内皮因子（VEGF）双功能克隆抗体，用于喉癌抗血管生成治疗。方法：采用二次杂交瘤技术制备抗人喉癌／抗VEGF双功能抗体。经酶联免疫吸附试验法和SP法检测喉癌及癌前病患者血清及癌组织中VEGF的含量表达。结果：获得6株分泌抗人喉癌／抗VEGF双功能抗体的杂交瘤，经免疫组化证实与喉癌细胞特异性结合率为93％，而与血管内皮细胞结合率为89％。血清中VEGF含量表达，喉癌组与癌前病组及正常对照组相比差异均显著。IgG亚型鉴定为IgG2aBSAb抗体效价为1：25 600倍（ELISA法）。结论：二次杂交瘤法制备的双功能抗体具有均匀性、可控性、效价高、稳定性好，可用于喉癌抗血管生成治疗，动态检测可作为判断喉癌预后的客观指标。     

抗Pgp/抗CD3双特异双链抗体的生物学活性研究

目的　研究抗Pgp 抗CD3双特异双链抗体介导的特异性靶向杀伤活性。方法　采用亲和层析法分离纯化本室构建的抗Pgp 抗CD3双特异双链抗体可溶性表达产物 ,并用SDS PAGE、Westernblot及抗活细胞间接免疫荧光法鉴定纯化产物 ;采用51 Cr释放试验测定其介导的体外靶向杀伤活性。结果　纯化的抗Pgp 抗CD3双特异双链抗体具有与Jurkat细胞 (CD3 )和K5 6 2 A0 2 (Pgp )细胞结合的活性 ;抗Pgp 抗CD3双特异双链抗体具有介导激活的T淋巴细胞杀伤Pgp表达阳性的耐药肿瘤细胞的作用 ,杀伤作用的强弱显示出效靶比和剂量依赖关系 ,且可被CD3ScFv或PgpScFv特异性的阻断。结论　抗Pgp 抗CD3微型双功能抗体有望成为治疗耐药肿瘤 ,特别是肿瘤残留灶和微小转移灶的治疗的一种新策略。     

4-1BBL胞膜外区蛋白增强抗CD3/抗PgP的抗肿瘤作用

目的研究4-1BBL胞膜外区蛋白对抗CD3/抗Pgp微型双功能抗体抗肿瘤作用的影响。方法表达纯化人4-1BBL胞膜外区融合蛋白及抗CD3/抗Pgp微型双功能抗体,体外CytoTox96检测联合应用人4-1BBL胞膜外区融合蛋白、抗CD3/抗Pgp微型双功能抗体及PBL对靶细胞K562/A02细胞的杀伤作用,体内建立裸鼠移植瘤模型检测4-1BBL胞膜外区蛋白作为一种免疫调节蛋白,增强抗CD3/抗Pgp基于PBL的抗肿瘤效果。结果4-1BBL胞膜外区融合蛋白在体外能够增强抗CD3/抗Pgp及PBL对靶细胞K562/A02的杀伤作用,在体内能够增强抗CD3/抗Pgp基于PBL的抗肿瘤作用。结论可溶型4-1BBL可能成为一种有前景的生物治疗佐剂,有助于PBL更高效地靶向杀伤肿瘤细胞。     

微型双功能抗体在裸鼠体内介导人T细胞杀伤白血病细胞

目的:研究抗CD3/抗CD19微型双功能抗体介导人T细胞对白血病细胞的特异性靶向杀伤活性。方法:利用Ficoll-Hypaque法分离外周血淋巴细胞(PBL),流式细胞术从中分选T淋巴细胞,FACS检测T细胞表面标记CD25和CD69激活后的表达变化,实时定量PCR检测各组穿孔素(Perforin)和颗粒酶A(Granzyme A)的释放,建立BALB/c裸鼠Raji细胞移植瘤模型,测定该双功能抗体介导的体内靶向杀伤活性。结果:激活的T细胞,双功能抗体组CD25和CD69的表达以及释放Perforin和Granzyme A的量均明显高于对照组,在对人白血病裸鼠移植瘤模型的生物治疗中,抗CD3/抗CD19微型双功能抗体能有效抑制白血病移植瘤的生长。结论:抗CD3/抗CD19微型双功能抗体在体外及动物肿瘤模型实验中能介导人T细胞有效杀伤白血病细胞,具有潜在的临床应用前景。     

抗CD3/抗CD20双特异双链抗体的生物学活性研究

目的研究抗CD3/抗CD20双特异双链抗体的生物学活性.方法采用亲和层析法纯化本室构建的抗CD3/抗CD20双特异双链抗体可溶性表达产物,并用SDS-PAGE,Westernblot和分子排阻层析鉴定纯化产物;采用FACS法和玫瑰花环试验测定纯化产物与靶细胞的结合活性;采用3H-TdR掺入实验和51Cr释放试验测定该双特异双链抗体的生物学性质.结果纯化的抗CD3/抗CD20双特异双链抗体具有与Jurkat(CD3+)和Daudi细胞(CD20+)的结合活性,且能同时与Jurkat和Daudi细胞结合形成玫瑰花环,并能竞争性封闭亲代鼠源性抗体HIT3a和HI47与Jurkat和Daudi细胞的结合位点;该双特异双链抗体具有促有丝分裂原作用和介导激活的T细胞杀伤Daudi细胞的活性.结论抗CD3/抗CD20双特异双链抗体具有与亲代鼠源性抗体HIT3a和HI47相同的性质,且能介导激活的T细胞杀伤表达CD20抗原的肿瘤细胞,是一个有望用于B细胞恶性肿瘤临床治疗的双特异性抗体.     

抗人CD138单克隆抗体以及重组双特异性抗体的开发及应用

目的制备鼠源抗人CD138单克隆抗体,经Western blot验证后,利用其基因序列构建重组抗人CD138抗体以及一种能够同时靶向CD138分子和CD3分子的双特异性抗体并对其功能进行验证。方法通过杂交瘤技术获得鼠源抗人CD138抗体,分子克隆构建重组抗体,Protein A纯化,综合运用Western blot(WB)、Flow cytometry(FC)、ELISA等实验方法进行相关的功能验证。结果鼠源的CD138单克隆抗体特异性强,可用于后续重组抗体的制备,而且重组的抗人CD138单克隆抗体经流式验证,同样可以与表达CD138的肿瘤细胞系(RPMI-8226,U266)进行结合,且不与CD138-的肿瘤细胞系(Jurkat)结合,在此基础上构建的双特异性抗体经功能验证,可以激活T细胞,从而对CD138+的细胞系进行特异杀伤。结论基于鼠源单克隆抗体重组构建表达的双特异性抗体anti-CD138×CD3具有靶向杀伤骨髓瘤细胞的生物活性,为细胞免疫治疗骨髓瘤疾病提供了临床研究基础。     

微型双功能抗体抗CD3／抗CD20的构建和表达

目的：构建和表达抗CD3／抗CD20微型双功能抗体,并测定微型双功能抗体的生物学活性。方法：采用PCR和overlap PCR方法构建抗CD3／抗CD20微型双功能抗体,并用双脱氧终止法测定DNA序列;采用亲和层析法纯化该产物,并用Western blot和分了排阻层析鉴定纯化产物;采用FACS法和玫瑰花环试验鉴定纯化产物与靶细胞的结合活性。结果：DNA序列测定结果表明：抗CD3／抗CD20微型双功能抗体已构建成功,表达可溶性产物的产量达1mg/ml以上,纯化产物中二聚体的比例达90％,具有与Jurkat(CD3^ 0和Daudi细胞（CD20^ ）结合的活性,且能同时与Jurkat和Daudi细胞结合形成玫瑰花环。结论：利用Diabody形式,首次成功地构建了抗CD3／抗CD20微型双功能抗体,并获得较高表达,表达产物具有与相应2个靶抗原结合的活性。     

免疫亲和层析法纯化抗Pgp/抗CD3双功能抗体

目的：制备可以纯化抗Pgp/抗CD3双功能抗体的免疫亲和层析柱。方法：纯化的抗抗CD3ScFv单克隆抗体与预活化的Sepharose4B偶联制成免疫亲和层析柱,采用自制的免疫亲和层析柱纯化由摇瓶发酵获得的抗Pgp/抗CD3双功能抗体,采用间接免疫荧光法测定抗CD3/抗Pgp微型双功能抗体能与Jurkat细胞及K562/A02细胞特异性结合活性。结果：成功地制备了可以纯化抗Pgp/抗CD3双功能抗体的免疫亲和层析柱,采用此柱纯化的抗体与Jurkat细胞及K562/A02细胞特异性结合的活性与带有E-tag纯化标志的抗体基本一致。结论：此介质可以替代价格高昂的E-tag亲和层析介质在纯化Pgp/抗CD3双特异双功能抗体中的应用,同时还可以避免由于E-tag纯化标志而带来的免疫原性问题,此项研究工作为抗Pgp/抗CD3双功能抗体将来在临床应用奠定了基础。     

CD3／抗CD20双特异双链抗体生物学活性研究

目的 研究抗CD3/抗CD20双特异双链抗体的生物学活性。方法 采用亲和层析法纯化本室构建的抗CD3/抗CD20双特异双链抗体可溶性表达产物,并用SDS-PAGE,Western blot和分子排阻层析鉴定纯化产物;采用FACS法和玫瑰花环试验测定纯化产物与靶细胞的结合活性;采用^3H-TdR掺入实验和^51Cr释放试验测定该双特异双链抗体的生物学性质。结果 纯化的抗CD3/抗CD20双特异双链抗体具有与Jurkat(CD3^ )和Daudi细胞（CD20^ )的结合活性,且能同时与Jurkat和Daudi细胞结合形成玫瑰花环,并能竞争性封闭亲代鼠源性抗体HIT3a和HI47与Jurkat和Daudi细胞的结合位点;该双特异双链抗体具有促进丝分裂原作用和介导激活的T细胞杀伤Daudi细胞的自学成才性。结论 抗CD3/抗CD20双特异双链抗体具有与亲代鼠源性抗体HIT3a和H147相同的性质。且能介导激活的T细胞杀伤表达CD20抗原的肿瘤细胞,是一个有望用于B细胞恶性肿瘤临床治疗的双特异性抗体。     

抗人卵巢癌×抗人CD3双特异单链抗体介导的效应细胞在体外对卵巢癌细胞的杀伤作用

目的　研究双特异单链抗体 (scBsAb)介导的Jurkat细胞 (CD3+ )及人外周血单个核细胞(PBMC)在体外对人卵巢癌细胞株SKOV3细胞的杀伤活性 ,从而探讨其用于卵巢癌治疗的可能性。方法以抗人卵巢癌×抗人CD3scBsAb激活效应细胞 ,以SKOV3为靶细胞 ,用MTT法测定不同实验条件下的杀伤活性。结果　 (1)以重组白细胞介素 2 (rIL 2 )、抗CD3单克隆抗体、抗CD2 8重链单域抗体 (VH)预刺激Jurkat及PBMC细胞比单纯用scBsAb激活效应细胞杀伤活性高 ;(2 )以Jurkat细胞或PBMC细胞作为杀伤细胞可得到相似的杀伤活性 ,最高杀伤率均在 75 %左右 ;(3)杀伤活性与scBsAb的浓度、作用时间及效靶比有关。对于Jurkat细胞 ,在抗体终浓度为 2 1μg ml,反应时间为 4 8h ,效靶比为 10∶1时达到最大杀伤率 74 .8% ;对于PBMC细胞 ,在抗体浓度为 2 0 μg ml,反应时间为 72h ,效靶比为 1∶1时达到最大杀伤率73.1%。 (4 )多因子联合应用能有效提高杀伤活性。结论　scBsAb在体外能够有效介导效应细胞杀伤肿瘤细胞 ,有明显的抗癌作用 ,具有潜在的应用前景。     

Use of an anti-CD16 antibody for in vivo depletion of natural killer cells in rhesus macaques

Non-human primates serve as key animal models for a variety of viral infections. To evaluate the contribution of natural killer (NK) cells to the immune-mediated control of these viruses in macaque monkeys, we have described a method for depleting NK cells in vivo by administration of anti-human CD16 mouse monoclonal antibody. Using a fluorometric NK-cell cytotoxicity assay, we show that most NK-cell cytotoxicity in rhesus monkey peripheral blood mononuclear cells resides in the CD16⁺ and/or CD159A⁺ subset of lymphocytes. The anti-human CD16 antibody, 3G8, binds to subsets of rhesus monkey lymphocytes and monocytes but not to neutrophils. Intravenous administration of 10–50 mg/kg of 3G8 to normal rhesus monkeys resulted in anti-CD16 antibody persistence in the plasma for 1–3 weeks. This treatment also depleted 80–90% of CD3^– CD159A⁺ lymphocytes, putative NK cells, from blood for at least 1 week and was associated with the loss of NK-cell cytotoxicity when evaluated by in vitro assays. Using this method, transient depletion of NK cells from two rhesus monkeys chronically infected with simian immunodeficiency virus failed to cause changes in virus replication. These studies describe a non-human primate model for in vivo NK-cell depletion and suggest a limited role for cytotoxic CD16⁺ NK cells in controlling AIDS virus replication during chronic infection.     

Loss of surface CD200 on stored allogeneic leukocytes may impair anti-abortive effect in vivo

PROBLEM: Prevention of spontaneous abortion by allogeneic mononuclear leukocyte immunotherapy has proven ineffective in the CBA x DBA/2 murine abortion model if the leukocytes are stored overnight before inoculation. The mechanism and generality of the phenomenon has not been elucidated. METHODS: As prevention of recurrent abortion in the CBA x DBA/2 model requires allogeneic BALB/c lymphoid cells bearing paternal antigens and the tolerance-signaling molecule CD200 (OX-2), we evaluated effects of cell storage on cell surface CD200 expression using flow cytometry of fresh or stored cells stained with monoclonal anti-CD200 antibody. Release of putative CD200 molecules into culture supernatant during storage was tested by the ability of supernatants to block binding of anti-CD200 to freshly isolated cells. Similar studies were done using human peripheral blood mononuclear leukocytes. Possible binding of soluble CD200 to immunoglobulin G (IgG) molecules in plasma as a basis for the anti-abortive effect of intravenous immunoglobulin G (IVIG) was tested using the standard peripheral blood lymphocyte (PBL) natural killer (NK) cell lysis of (51)Cr-labeled K562 cells and monoclonal anti-human CD200 antibodies. RESULTS: Loss of anti-abortive effect of BALB/c cells with overnight storage at 4 degrees C and blocking of protective effect of freshly isolated cells with anti-CD200 antibody was confirmed. Supernatants of stored cells acquired a low level of protective activity against abortion in the CBA x DBA/2 model. Cell surface CD200 was lost with overnight storage at 4 or 22 degrees C, and supernatants acquired the ability to block binding of anti-CD200 antibody to fresh cells. Similar results were obtained using human PBL. However, if cells were stored overnight in IgG containing plasma, binding was not blocked. Suppression of NK cell lysis by PBL was abrogated if anti-CD200 antibody was added to the assay. CONCLUSIONS: Loss of the tolerance signal CD200 from allogeneic cells occurs with storage overnight, and their ability to protect against abortion is lost. CD200 appears to be shed into the supernatant, and may associate with IgG molecules rendering IVIG suppressive.     

抗抗CD3 ScFv单克隆抗体的制备及鉴定

目的：制备抗抗CD3 ScFv单克隆抗体并研究其生物活性.方法：分离纯化后的抗CD3 ScFv蛋白免疫BALB/c小鼠,采用传统杂交瘤技术制备抗抗CD3 ScFv单克隆抗体;采用ELISA和Western blot鉴定其亚类和抗原结合特异性;采用FACS测定抗抗CD3 ScFv单克隆抗体对Jurkat细胞特异活性.结果：成功筛选出一株能稳定分泌抗抗CD3 ScFv单克隆抗体的杂交瘤细胞株（10B7）,其分泌的抗体亚类为IgG1.该抗抗CD3 ScFv单克隆抗体直标后可特异性结合抗CD3 ScFv蛋白和抗CD3抗体.结论：文中所研制的抗抗CD3 ScFv单克隆抗体具有与抗CD3抗体、抗CD3 ScFv蛋白特异结合的活性,在肿瘤导向治疗中抗CD3/抗肿瘤双特异抗体的亲和层析纯化、药代动力学监测等方面具有广泛的应用前景.     

Specific activation of resting T cells against tumour cells by bispecific antibodies and CD28-mediated costimulation is accompanied by Th1 differentiation and recruitment of MHC-independent cytotoxicity

Specific activation of resting lymphocytes for tumour targeting can be achieved by bispecific monoclonal antibodies (bi-MoAbs) with specificity for tumour antigens and T cell-activating antigens in combination with a costimulatory anti-CD28 antibody. In this study we focus on the immunomodulatory function of an anti-CD3/CA19-9 bi-MoAb in combination with a costimulatory anti-CD28 antibody which may result not only in antigen-specific, T cell-mediated tumour cell lysis but also in recruitment of other cellular effector functions. In combination with costimulatory anti-CD28 antibodies, resting peripheral lymphocytes could be activated specifically to secrete high amounts of Th1 cytokines (IL-2, interferon-gamma (IFN-γ)) characterizing a cellular immune response. In contrast, no IL-4 and only low amounts of IL-10 could be detected. Furthermore, bi-MoAb-mediated CA19-9-specific activation of T cells was accompanied by recruitment of MHC- and CA19-9-independent cytotoxicity, as was determined by lysis of different CA19-9⁻cell lines. This MHC-independent cytotxicity was mediated at least in part by activated natural killer (NK) cells, as depletion of CD16⁺ NK cells resulted in substantial decrease of cytotoxicity against CA19-9⁻ targets. Our results indicate that specific activation of resting T cells with CD3-associated bi-MoAbs in combination with an anti-CD28 antibody leads to a Th1 differentiation pathway and is accompanied by recruitment of MHC-independent lymphokine-activated killer (LAK) cell cytotoxicity which can possibly be directed against a heterogeneous tumour.     

Cytotoxic difference of T cells expanded with anti-CD3 monoclonal antibody in the presence and absence of anti-CD 28 monoclonal antibody

Bulk T cells can be expanded by CD3 stimulation alone (CD3-Ts) or by CD3/CD28 dual stimulation (CD3/CD28-Ts) of peripheral blood mononuclear cells (PBMC). However, few reports have described the difference of features between CD3-Ts and CD3/CD28-Ts. PBMC were stimulated with anti-CD3 monoclonal antibody (mAb) alone or co-stimulated with anti-CD3/CD28 mAbs immobilized on plastic plates, in the presence of rhIL-2 for 4 days, subsequently cultured in the presence of rhIL-2 with no antibody then analyzed. The expansion rate was significantly lower for CD3-Ts (965 + 510-fold, n=5) than CD3/CD28-Ts (2263 + 856-fold, n=5) (p<0.05). The CD4/CD8 ratio, the percentage of CD28(+) cell, and the percentage of T cells with no ability to generate intracytoplasmic interleukin-4 (IL-4) or interferon-gamma (IFN-gamma) were all significantly higher, but, phenotypically, memory cells were lower in CD3/CD28-Ts than in CD3-Ts. The levels of activity of both natural killer (NK) and lymphocyte-activated killer (LAK) cells were lower in CD3/CD28-Ts than CD3-Ts. In comparison to CD3-Ts, CD3/CD28-Ts showed impaired migration toward RANTES. In conclusion, T cells expanded with anti-CD3 and anti-CD28 mAbs differ from those expanded with anti-CD3 alone with proliferation, cytotoxicity, chemotaxis, and phenotype. These differences may exert profound influences on the therapeutic potential of output cells.     

Immunohistochemical characterization of lymphosarcoma in two alpacas (Lama pacos)

Species cross-reactive anti-peptide antibodies were assessed in formalin-fixed tissue for use in immunophenotyping of lymphosarcoma in two alpacas. Diagnosis of lymphosarcoma was made by routine histopathological examination. Primary antibodies used for immunophenotyping were anti-human CD3 and anti-human CD5 for T cells; and anti-human CD79a and anti-human CD79b for B cells/plasma cells. In one case, most of the neoplastic cells were labelled with both anti-CD3 and anti-CD79b, and smaller numbers were labelled with anti-CD79a. The other case was classified as a B-cell tumour on the basis of labelling of the majority of neoplastic cells with anti-CD79b and anti-CD79a. This is the first recorded attempt at immunophenotyping lymphosarcoma in alpacas and, to our knowledge, the first record of presumptive co-expression of T- and B-cell-associated molecules in lymphosarcoma in the veterinary literature.     

抗人PD-L1 单克隆抗体的制备及其应用

目的:获得能应用于临床诊断以及阻断PD-L1 与PD-1 结合的抗人PD-L1 单克隆抗体。方法:采用重组表达的人PD-L1 蛋白免疫BALB/ c 小鼠,通过杂交瘤细胞融合技术获得稳定分泌抗人PD-L1 单抗的阳性细胞株,ELISA 方法鉴定抗体的特异性、亲和力、亚型等方面特性;免疫印迹、间接免疫荧光方法对肿瘤细胞进行检测;肿瘤杀伤实验验证抗体阻断活性。结果:共获得2 株抗人PD-L1 单抗,抗体效价分别为1 2.56 106 和1 3 105 ,亲和力分别为1.5 109 L/ mol 和2.5 108 L/ mol,均与PD-L2 蛋白无交叉反应。免疫印迹、间接免疫荧光证实抗体有诊断作用。杀伤实验显示抗体有阻断作用。结论:共获得两株稳定分泌高效价、高特异性的抗人PD-L1 单抗的杂交瘤细胞株,能作为诊断抗体应用于肿瘤表型检测和预后有效性的评估。抗体的阻断功能可应用于联合CIK 细胞免疫治疗。     

抗人CD134单抗对外周血单个核细胞穿孔素mRNA表达的影响

目的： 观察不同浓度抗人CD134单抗对外周血单个核细胞穿孔素mRNA表达的影响及时间效应，旨在探讨抗人CD134单抗延长T细胞存活的可能机制。 方法: 应用反转录-聚合酶链反应(RT-PCR)技术分别检测不同浓度（1 mg/L、5 mg/L、10 mg/L）抗人CD134单抗对外周血单个核细胞穿孔素mRNA表达的影响，同时检测每种浓度作用不同时间（6 h、12 h、24 h、48 h）对外周血单个核细胞穿孔素mRNA表达的影响。 结果: 不同浓度CD134单抗作用不同时间，对人外周血单个核细胞穿孔素mRNA表达均有不同程度抑制作用，在 24 h 该作用达高峰。当CD134单抗浓度﹥5 mg/L时，这种抑制作用不再增强（P>0.05）。 结论: 抗人CD134单抗可在转录水平抑制穿孔素表达，该效应在 24 h 达高峰且会饱和，此乃抗人CD134单抗延长T细胞存活的主要机制。     

抗人CD3单链抗体/p53四聚功能域融合基因的构建及表达

目的：构建抗人CD3单链抗体(scFv)／p53四聚功能域融合基因，并进行真核表达及活性测定。方法：在已经构建抗人CD3 scFv和人IgG3上游铰链区／p53四聚功能域融合基因基础上，将抗人CD3 scFv克隆入载体pUC18／IgG3／p53中，构建抗人CD3 scFv／p53四聚功能域融合基因。经酶切鉴定及序列测定证实后，将融合基因克隆入真核表达载体pSecTag2-B中，并转染Hela细胞进行表达。表达产物纯化后，利用流式细胞仪进行活性测定。结果：获得了抗人CD3 scFv／p53四聚功能域融合基因，基因全长为882 bp，可编码294个氨基酸，与已发表的抗人CD3 scFv、人IgG3上游铰链区和人p53四聚功能域基因cDNA序列相一致。表达产物经SDS-PAGE和Western blot证实，为Mr约35000的特异蛋白条带。纯化后经流式细胞仪检测，可特异性地结合人外周血单个核细胞(PBMC)，亲和力高于scFv。结论：获得了可与PBMc特异性结合的抗人CD3 scFv四聚体，为进一步临床应用奠定了基础。     

Adhesion molecule-mediated signals regulate major histocompatibility complex-unrestricted and CD3/T cell receptor-triggered cytotoxicity.

Appropriate experimental conditions were devised to demonstrate that CD58 (LFA-3), CD54 (ICAM-1) and CD11a/CD18 (LFA-1) adhesion molecules are the source of signals that regulate nonspecific major histocompatibility complex-unrestricted and CD3/T cell receptor (TcR)-triggered cytotoxicity. Using anti-LFA-3 monoclonal antibody (mAb)-treated, interleukin-2 (IL-2)-cultured peripheral blood lymphocytes (PBL) or cloned CD3+/CD8+ cells as lymphocyte-activated killer (LAK) effectors, and ligand (CD2)-negative tumor cell lines as targets, a down-regulation of CD3- and CD3+ cell-mediated LAK activity was consistently observed. Anti-LFA-3 mAb also down-regulated tumor cell lysis when T cell clones were triggered to kill P815 cells through stimulation of the CD3/TcR complex by an anti-CD3 mAb. The inhibitory effect of anti-LFA-3 mAb was not prevented by stimulatory anti-CD2 mAb. Anti-ICAM-1 mAb treatment of IL-2-cultured PBL consistently up-regulated LAK cytotoxicity against tumor target cells. However, this effect was only exerted on CD3- LAK effectors. Anti-LFA-1 mAb blocked conjugate formation between effector cells and tumor target cells, thus rendering this model unsuitable to evaluate the regulatory role of LFA-1. Therefore, a cytotoxicity model system was applied in which a hybrid anti-CD3/anti-human red blood cell (HuRBC) mAb triggers cytolytic T cells to lyse HuRBC. In these experiments, anti-LFA-1 mAb markedly up-regulated the lytic ability of IL-2-cultured PBL. We conclude that mAb against LFA-3, ICAM-1 and LFA-1 molecules deliver regulatory signals for LAK cells and cytotoxic T lymphocytes. As these stimuli may be delivered by ligands expressed on tumor targets as well as on other immune competent and inflammatory cells, the present observations are relevant in the context of both the host's immune response against tumors and the general functioning of the immune system.