In vitro growth of cytotoxic human lymphocytes. V. Generation of allospecific cytotoxic lymphocytes to nonimmunogenic antigen by supplementation of in vitro sensitization with partially purified T-cell growth factor

TCR-independent cytokine stimulation induces non-MHC-restricted T cell activity and is negatively regulated by HLA class I

Recent evidence suggests that the functional status of T cells activated independently from their TCR differs substantially from classical MHC-restricted T cells. Here, we show that TCR-independent, short-term stimulation via the common gamma-chain of the IL-2/IL-15 receptor induces non-MHC-restricted cytotoxicity and sustained cytokine secretion in purified CD4+ or CD8+ T cells. NK-like cytotoxicity is directed against MHC class I-negative targets and can be inhibited by classical and non-classical HLA class I molecules. Known inhibitory receptors, such as CD85j (ILT2) and leukocyte-associated Ig-like receptor-1, are not responsible for this HLA-mediated inhibition. NK-like cytotoxicity can be costimulated by NKG2D (CD314) triggering, but 2B4 (CD244) and DNAM-1 (CD226) are not involved. NK-like T cells display an activated phenotype and secrete various cytokines, including IFN-gamma, TNF-alpha, IL-5, IL-13 and MIP-1beta. Under normal conditions, HLA class I-mediated inhibition may function as a safety mechanism to prevent unbalanced cytokine production and effector killing mechanisms by T cells that were activated independently from their TCR. Non-MHC-restricted activity represents a functional status rather than a property of distinct T cell subpopulations. Thus, cytokine-induced, non-MHC-restricted T cells may be relevant in immune responses against tumors showing aberrant MHC expression through their capacities of cytokine production and direct tumor cell eradication.

The IL-2 mediated amplification of cellular cytotoxicity

High dose [greater than 1 nM or 30 IU] interleukin-2 (IL-2) can induce MHC-unrestricted killing from various lymphoid populations. Although it is well established that CD16+ NK cells are the major source of blood-derived LAK precursors, other lymphoid cells, including several CD3+ T subsets can be a source of precursor activity. We hypothesize that most, if not all, lymphocytes with cytolytic potential may eventually express MHC-unrestricted killing, when provided with adequate IL-2 to initiate required secondary cytokine production. This perspective article presents our cumulative data supporting the role of secondary cytokines in the IL-2 initiated activation of MHC-unrestricted killing, first by our observations of synergy with the exogenously added TNFs or IL-1s in combination with low dose IL-2, and then by the evidence of endogenous cytokine production and response in lymphocytes stimulated with high dose IL-2. Understanding the amplification mechanism(s) of the various effector arms of the immune system is critical to the eventual regulation of graft rejection, autoimmune phenomena, and potentially to the treatment of cancer. Our studies have focused on the cytotoxic lymphocyte effector system, and have addressed the molecular pathways by which IL-2 induced cytokines influence the quantity and quality of the cytotoxic lymphocyte response. This article will review the pivotal role that IL-2 plays in the development of CTL (MHC-restricted antigen-specific cytotoxic lymphocytes), followed by the description of how studies in the CTL system led to the observation that IL-2 alone can activate a heterogeneous collection of MHC-unrestricted killer lymphocytes, originally known as "Lymphokine Activated Killers" or LAK.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytological characteristics of human glioma-infiltrating lymphocytes stimulated with recombinant interleukin 2 and an anti-CD3 antibody

Tumor-infiltrating lymphocytes (TIL) were generated from 10 glioma specimens by using recombinant interleukin-2 and an anti-CD3 antibody (CD3 + TILs). We obtained more than 1 x 10(9) cells in 5 cases, more than 5 x 10(8) cells in 2 cases, and about 1 x 10(8) cells in 3 cases during three weeks of incubation from small specimens ranging in weight from 0.5 to 2.0 g. In 4 cases, TILs were expanded following stimulation with only rIL-2 (CD3-TILs). The growth rate of CD3-TILs was less than that of CD3 + TILs. Cytotoxicity of CD3 + TILs was lower than that of lymphokine-activated killer (LAK) cells in a standard 4h 51Cr release assay. Cold target inhibition was undertaken in three cases and specific cytotoxicity could be shown in only one case. CD3 + TILs mainly consisted of CD3-positive cells, ranging from 63.2 to 99.9%. The ratio of CD4-positive cells to CD8-positive cells was not constant. The expression of Leu 7 and CD16 was low. The present study did not confirm previous findings that TILs were more tumor-selective and potent than LAK cells. Furthermore, the results on in vitro antitumor activity of those cells were not necessarily consistent with the results on their clinical activity. Further careful work is necessary on the preparation of immunocytes and the subsequent adoptive immunotherapy.

Immunotherapy for malignant glioma using human recombinant interleukin-2 and activated autologous lymphocytes. A review of pre-clinical and clinical investigations

Over the past few years, we and a number of other groups have conducted laboratory experiments and clinical trials of human recombinant interleukin-2 (rIL-2) alone or in combination with autologous 'activated' lymphocytes expressing in vitro tumoricidal activity in order to define toxicity and indicate its potential efficacy in patients with high-grade glioma. Because high rIL-2 concentrations can be attained with considerably less toxicity than with a systemic approach, all of the clinical trials, to date, have chosen a direct route; injecting lymphokine and cells into tumor tissue, the cystic cavity remaining after tumor excision, and/or neural parenchyma surrounding the site of tumor excision. While the rIL-2 therapies, as they have been applied in animal glioma models and patients, are safe, cerebral edema around the site of treatment has been a consistent finding. We have also seen, however, that steroid medications used by patients to control their cerebral edema may depress the anti-tumor activity of rIL-2 by depressing the capacity of lymphocytes to develop normal LAK activity. Although none of the immunotherapies involving rIL-2 have produced cures, the fact that sustained clinical responses have been reported, suggests that such therapies may slow a recurrence of tumor at the site of treatment. Efforts to improve outcome from rIL-2--based immunotherapies for malignant glioma are continuing with manipulation of rIL-2 dosing and scheduling and also with combinations of rIL-2 and other recombinant cytokines.

Therapeutic uses of interleukin-2 and lymphokine-activated killer (LAK) cells

Interleukin-2 (IL-2) is the first of a growing list of lymphokines to be cloned and available for preclinical and clinical evaluation. A product of T-helper lymphocytes, IL-2 augments the cytolytic activity of T-lymphocytes and natural killer (NK) cells, stimulates the proliferation of these cells, and induces the formation of lymphokine-activated killer (LAK) cells. LAK cells exhibit cytolytic activity against a broad range of both freshly isolated and cultured tumor cells, while exhibiting limited cytolytic activity against normal cells. The apparently large therapeutic index suggested by in vitro studies is strongly supported by the antitumor responses seen in preclinical studies. Initial clinical studies reported encouraging response rates, but the actual role of IL-2 and/or LAK cell infusion in cancer therapy has yet to be determined, and may only represent the first step in managing the tumoricidal potential of the immune system.

Human lymphokine-activated killer cells (LAK cells) as a potential immunotherapeutic modality

Lymphokine-activated killer cells (LAK) are cytolytic lymphocytes with the unique capacity of killing NK-resistant fresh human tumor cells in short-term assays. LAK appear to kill autologous tumors as well as TNP-modified self and allogeneic tumors with complete crossreactivity, both at the population and clonal level. Initial studies on the classification of LAK conclude that LAK are distinct from the classical NK and T-lymphocyte systems based on a number of criteria including surface phenotype, activation conditions, and spectrum of susceptible target cells. LAK kill rasoncogene-transfected fibroblasts in a manner similar to fresh tumors. As yet, the target cell determinant responsible for susceptibility to LAK lysis is unknown, but cell-surface proteins are definitely involved. Activation of LAK requires only IL-2, and is most efficient using serum-free conditions. Because interleukin-2 alone is sufficient for LAK activation, we have tested in vitro whether fresh PBL could be activated in the presence of tumor, as might be desired in vivo. LAK activation was greatly suppressed by tumor presence. LAK activation is also suppressed by hydrocortisone, but not cyclosporine A. Because of the above and other findings, we have initiated a clinical protocol to test whether LAK made from brain-tumor patients' PBL could eliminate residual glioma tumor cells. Autochthonous LAK, plus rIL-2 to maintain lytic ability, are injected during surgery. Preclinical studies in a rat glioma model have shown this approach to be safe. Eleven glioma patients have been injected intracerebrally with IL-2 and/or LAK with no immediate or long-term (14 months follow-up) adverse effects. Much work is needed to understand the LAK phenomenon and to resolve its potential usefulness in cancer therapy as well as its inherent biologic role.

Human recombinant interleukin-2 augments in vitro blastogenesis of bovine and porcine lymphocytes

The recent cloning of the human gene encoding interleukin 2 (IL-2) has provided the means for economical production of large quantities of the pure lymphokine for clinical studies. Human recombinant interleukin 2 (HrIL-2) has been reported to have in vitro and in vivo immunomodulating effects in the murine system, suggesting the cloned gene product has cross-species activity. Bovine and porcine peripheral blood lymphocytes were tested for responsiveness to HrIL-2 in a lymphocyte blastogenesis assay. Not only was the HrIL-2 highly stimulatory but it also reconstituted lymphocyte responsiveness to maximal values following incubation with suboptimal concentrations of mitogen plus exogenous lymphokine. These studies suggest that HrIL-2 has the potential of serving as an in vivo modulator of immunoresponsiveness in domestic species. The contribution to food animal medicine will be considerable if administration of the lymphokine results in augmentation of antigen-specific immune responses when applied as an adjuvant, non-specific booster of pre-existing immunity, or for therapy of immunosuppression.

Characterization of culture-induced cytotoxicity from human peripheral lymphocyte subpopulations

Cultured human lymphocyte subpopulations can generate cytotoxicity against K562 leukemia target cells under certain conditions. Such cytotoxicity arises during mixed leukocyte culture or in medium containing fetal calf serum (FCS), mitogenic factors, or interleukin 2. We cultured peripheral blood lymphocytes (PBL) in FCS-containing medium after fractionation of these cells on a Percoll discontinuous density gradient. Higher density cell fractions generated culture-induced spontaneous cytotoxicity (CIC) after 2-3 days in culture. CIC was not due to a loss of suppressor cells during fractionation since culture of PBL prior to fractionation yielded the same results. At least some CIC was associated with the differentiation of higher density cells to newly appearing lower density cells during culture. Most CIC required cells with the HNK-1- OKT3- OKM1+ phenotype. Culture-induced cytotoxicity has some similarities to the previously described lymphokine-activated killing but some important differences are also discussed.

The human lymphokine-activated killer cell system. V. Purified recombinant interleukin 2 activates cytotoxic lymphocytes which lyse both natural killer-resistant autologous and allogeneic tumors and trinitrophenyl-modified autologous peripheral blood lymphocytes

Culture of human peripheral blood lymphocytes (PBL) in purified natural or recombinant interleukin 2 in the absence of exogenous antigen or mitogen causes the differentiation of nonlytic precursor cells into lymphokine-activated killers (LAK). A titration of purified Jurkat IL-2 (BRMP, FCRC, NIH) IL-2 showed that the relatively low concentration of 5 U/ml was optimal for LAK activation. When the responding PBL were pretreated with either mitomycin C or gamma irradiation, LAK activation did not occur, indicating that proliferation, in addition to differentiation, is required. The spectrum of target cells susceptible to LAK lysis in a 4-hr chromium-51-release assay includes fresh NK-resistant tumor cells and trinitrophenyl (TNP)-modified autologous PBL. Unmodified PBL are not lysed. Cold target inhibition studies indicated that LAK lysis of autologous TNP-PBL is totally inhibited by fresh tumors cells, and that tumor lysis is inhibited by TNP-PBL. Additionally, allogeneic tumors totally inhibit lysis of autologous tumor cells in other cold target studies. These results demonstrate that the lytic activity expressed by LAK is not HLA restricted, is not limited to tumor cells, and is "polyspecific" as indicated by the cross-reactive recognition of multiple target cell types in these cold target inhibition studies.

Biological activity of recombinant human interleukin-2 produced in Escherichia coli

The gene for interleukin-2 was isolated from the Jurkat cell line and from normal peripheral blood lymphocytes and, when inserted in Escherichia coli, was expressed at high concentrations. This interleukin-2 was purified to apparent homogeneity and tested for biological activity in a variety of assays in vitro and in vivo. The recombinant lymphokine supports the growth of murine and human interleukin-2 dependent cell lines, enhances the generation of murine and human cytolytic cells in vitro, and generates lymphokine activated killer cells from murine and human lymphocytes. It has a serum half-life of 2 to 3 minutes in the mouse and significantly enhances the generation of cytolytic cells in vivo after alloimmunization. No functional differences between native and the recombinant interleukin-2 molecules have been detected.

Transformation of different phenotypic types of human bone marrow T-lymphocytes by HTLV-1

Fresh bone marrow mononuclear leukocytes were used as a target for infection by human T-cell leukemia-lymphoma virus subgroup 1 (HTLV-1) by co-cultivation with virus-positive cell lines. The lines were established from T-cell leukemia-lymphoma patients or HTLV-1-transformed human umbilical cord-blood T cells. Clumps of transformed cells became visible by 2-3 weeks after infection and developed at a high frequency (greater than 90%) in the bone marrow samples used. Stimulation of target cells with lymphocyte mitogens facilitated this process but was not absolutely required. Unlike fresh or cultured cells from HTLV-1-positive adult leukemia-lymphoma patients and HTLV-1-transformed cord-blood T cells, which usually have an OKT 4/leu 3a surface phenotype, the transformed bone marrow cells frequently fell into one of three categories based on their reactivity with cell-specific monoclonal antibodies. These included populations of cells that were predominantly; (1) OKT 4/leu 3a-positive, (2) OKT 8/leu 2a-positive, and (3) cells expressing neither phenotype. Fresh bone marrow provided a rapid and efficient system for the assessment of HTLV-1 infection. The type of bone marrow cells transformed in vitro suggests that HTLV-1 can infect several subsets of T lymphocytes, possibly including immature cells or that these cells can undergo phenotypic modulation.

Lymphokine-activated killer cell phenomenon. II. Precursor phenotype is serologically distinct from peripheral T lymphocytes, memory cytotoxic thymus-derived lymphocytes, and natural killer cells

Culture of human peripheral blood lymphocytes (PBL) in partially purified and lectin-free interleukin 2 results in the generation of cytotoxic effector cells which have the unique property of lysing natural killer (NK)-resistant fresh human tumor cells. We have termed these effector cells "lymphokine- activated killer" cells (LAK). LAK are generated from both normal and cancer patients' PBL and are able to lyse both autologous and allogeneic tumor cells from all histologic tumor types tested. Our previous studies suggested that the LAK phenomenon was distinct from either the cytotoxic thymus-derived lymphocyte (CTL) or NK systems based on a variety of criteria. This study reports that the cell type involved is also distinct, as determined by phenotypic characteristics. The LAK effector cell phenotype was analyzed in parallel with alloimmune CTL, and LAK were found to be similarly susceptible to the monoclonal anti-T cell antibodies OKT-3 or OKT-8 plus complement. In contrast the LAK precursor was not susceptible to the OKT-3 or Leu-1 antibodies plus complement, while the ability to generate alloimmune CTL was totally obliterated when tested using the same PBL responder population; in fact, generation of LAK was found to be augmented five- to sixfold, clearly suggesting that LAK precursor cells are not T lymphocytes as defined by these antibodies. LAK precursors were found to be abundant in NK cell-enriched Percoll gradient fractions, which had been depleted of the 29 degrees C E- rosetting "high affinity" T cells. However, LAK precursors were found to be distinct from the majority of NK cells since lysis of fresh PBL with the monoclonal antibodies OKM-1, Leu-7, or OKT-11 significantly depleted or totally eliminated NK activity, while subsequent activation of the remaining cells generated high levels of LAK and in some cases augmented levels of LAK. LAK precursors were found to be distributed in the thymus, bone marrow, spleen, lymph node, and thoracic duct in addition to the PBL. Therefore, while the cell(s) responsible for activation and expression of LAK activity have some common features with the classic T cell-mediated CTL and NK cell systems, the LAK precursor cells are clearly distinct as determined by phenotype analysis using monoclonal antibodies and complement, and at present must be classified as a "null" cell.

Lysis of fresh human solid tumor cells by autologous lymphocytes activated in vitro by allosensitization

We have previously demonstrated that cancer patients' peripheral blood lymphocytes (PBL) allosensitized against single or pool normal donor PBL are capable of lysing fresh autologous tumor cells in a 4-h 51Cr-release assay. In this report, we present further investigations into this phenomenon. These alloactivated killer cells (A-AK cells) lysed autologous and allogeneic tumors and allogeneic but not autologous PBL. Furthermore, cold target inhibition studies demonstrated that autologous and allogeneic tumors were lysed by the same effector cells. Multiple metastases from the same patient were equivalently lysed by these A-Ak cells. The presence of adherent cells and proliferation of the precursors were necessary to generate A-AK cells, although the effector cell itself was radioresistant and nonadherent. The effects of allosensitization were enhanced by the addition of lectin-free interleukin-2 preparations to the in vitro culture by partial depletion of adherent cells prior to sensitization. The A-Ak effector cell was OKT3+, OKT8+, OKT4-, OKM1- and could be generated by just 3 days of allosensitization. The precursors for A-Ak cells could be separated from NK cells on percoll gradients and lysis could be generated from thoracic duct lymphocytes, a population devoid of NK cells. The phenotype of the majority of the precursor cells was OKT3+, OKT4-. Theses alloactivated PBL could be expanded in crude or lectin-free interleukin-2 without loss of cytotoxicity for fresh autologous tumor cells. Activated T cells represent a population of on-NK cells with broad lytic specificity for fresh tumor cells. Such cells may be of value in the adoptive immunotherapy of human solid tumors and may play a role in immune surveillance.