Exposure to golimumab during pregnancy: Results from the Company's global safety database.

Data on the use of golimumab (GLM) during pregnancy are limited. This study evaluated pregnancy outcomes in women treated with GLM during pregnancy. Cumulative data on GLM-exposed pregnancies from the Company's global safety database (GSD) are summarized. Cases were medically confirmed maternal exposures to GLM during pregnancy or within 3 months prior to conception with a reported pregnancy outcome. Pregnancy outcomes (e.g., live births) and congenital anomalies in prospectively reported cases (i.e., pregnancy outcome not known when first reported to the company) are presented in a descriptive manner. As of May 31, 2022, 261 prospectively reported pregnancies exposed to GLM were reported in the GSD: 214 (82.0%) live births (including six sets of twins), 31 (11.9%) spontaneous abortions (including one set of twins), 13 (5.0%) induced/elective abortions, 2 (0.8%) reported intrauterine death/still birth, and 1 (0.4%) fetal adverse event in an ongoing pregnancy. The majority of pregnancies had exposure to GLM at least in the first trimester of pregnancy. In total, seven congenital anomalies (7/261; 2.7%) were reported. Of these seven congenital anomalies, five were considered major according to EUROCAT classification version 1.4. Among the five prospectively reported congenital anomalies noted in live births (5/214; 2.3%), four were classified as major (4/214; 1.8%). The rates of adverse pregnancy outcomes and major congenital anomalies in prospectively reported pregnancy cases with exposure to GLM in the Company's GSD were consistent with published background rates for the general population.

Drug Utilization Studies in Pregnant Women for Newly Licensed Medicinal Products: A Contribution from IMI ConcePTION.

Purpose: Studies focusing on safety outcomes typically require large populations to comprehensively characterise the patient groups exposed to the medicines under investigation. However, there is often less information for subpopulations, such as pregnant or breastfeeding women, particularly when new medicines are considered. It is important to understand what information can be obtained from drug utilization studies (DUS) involving pregnant women in the early years postmarketing to provide supportive information for safety studies. The aims of this literature review are to (1) identify and review DUS for new medicines in pregnancy and breastfeeding and (2) list and summarise key information items to be reported in a DUS for new medicines in pregnancy. Methods: To identify postmarketing DUS of new prescription medicines or enantiomers in pregnancy, a systematic literature review was undertaken in PubMed and Embase between January 2015 and June 2022. In addition, the complete database of the ENCePP EU PAS Register was systematically searched to June 2022. Results: We identified 11 published DUS on new medicines in pregnancy from the ENCePP EU PAS Register and none from other sources. No studies on breastfeeding were identified. The 11 identified publications reported the medicine's use for the first 3 to 5 years after marketing approval. No reports assessed utilization in the first 3 years of approval. It was usual to issue interim reports annually (7 studies). All studies concerned conditions managed in ambulatory care (primary care and outpatient facilities) and included some primary care prescribing. Most (n = 8) only had prescribing/dispensing data available at individual level for ambulatory care; outpatient prescribing was included in three of these studies Three studies held a limited amount of in-hospital prescribing data. A DUS can confirm at an early stage whether there are sufficient exposed pregnancies in available data sources to ensure a safety study is powered to detect a difference in the prevalence of adverse pregnancy or infant outcomes or if additional data from other databases are needed. A DUS may also help address methodological considerations such as selection of comparators. DUS can be performed embedded in a DUS in the general population, in a cohort of women of childbearing age, or in a cohort of pregnant women. Conclusion: This review summarises key aspects of a DUS for new medicines in pregnancy. DUS for new medicines in pregnancy should be planned before marketing, scheduled for the first 3 to 5 years after release, with annual interim/progress reports, and reported in peer-reviewed journals. By offering detailed information on data sources, exposure timing, prevalence and location, coprescribing, comorbidities, coexposures, and demographics, a DUS will offer a firm foundation for safety studies and will help to contextualize spontaneous reporting of serious adverse events.

Landscape review of global real-world data sources for studying medication use in pregnancy and lactation that support regulatory decision making.

PURPOSE: Most pregnant people take at least one medication during gestation or while breastfeeding, however data are lacking on the safety of medication use in these populations. We conducted a landscape review of real-world data sources specific to medication use in pregnancy and breastfeeding populations that have met, or have potential to meet, health authorities' requirements for post-authorization safety studies. METHODS: A 2-phase approach identified data sources from literature, publicly available registers of non-interventional post-authorization studies of pregnant women, existing database inventories, and emerging data sources known to the authors. RESULTS: Required key attributes were assessed according to current regulatory guidance, resulting in selection of 49 suitable data sources. All global regions were represented, with North America (37%) and Europe (33%) most common; 12% of the data sources included pregnancy information from low-to middle-income countries. Administrative healthcare claims (25%) and electronic healthcare records (21%) comprised the largest types of data sources. Across data sources, 53% were managed by national or regional governments, 27% by industry, and 20% by academic institutions. Maternal age, diagnoses, prenatal care, and reproductive history were available in most, whereas fewer included demographic data (e.g., race/ethnicity). Breastfeeding data were collected in 37% of the final data sources. CONCLUSION: We conducted a systematic approach to data source evaluation of pregnancy and breastfeeding to be used as a resource for investigators to consider when designing pregnancy-related research studies to satisfy regulatory requirements.

Pregnancy outcomes following periconceptional or gestational exposure to ustekinumab: Review of cases reported to the manufacturer's global safety database.

BACKGROUND: Ustekinumab, a human immunoglobulin G1 monoclonal antibody that binds to and inhibits interleukin (IL)-12/IL-23, is indicated for multiple immune-mediated diseases. Ustekinumab is actively transported across the placenta and theoretically could impact pregnancy outcomes. Limited data on pregnancy outcomes with ustekinumab exposure are available. AIM: To assess pregnancy outcomes in patients exposed to ustekinumab during pregnancy METHODS: Cumulative data on medically confirmed ustekinumab-exposed pregnancies from the manufacturer's Global Safety Database were summarised. Descriptive data for pregnancy outcomes were presented overall and by patient subgroups. RESULTS: As of 31 August 2020, 408 medically confirmed, prospective, maternal ustekinumab-exposed pregnancies with reported outcomes were identified. The mean maternal age was 31 years. Of the 420 pregnancy outcomes (including 4 sets of twins),a , b 340 (81%) were live births, 51 (12.1%) spontaneous abortions, 25 (6%) elective/induced abortions, 3 (0.7%) stillbirths and 1 (0.2%) ongoing pregnancy with foetal congenital anomaly (CA). Among 340 live births, 33 (9.7%) were born pre-term. The rate of major CAs was similar by indication (Crohn's disease vs psoriasis), ustekinumab dose (45 mg vs 90 mg) and timing and duration of maternal exposure to ustekinumab. Prospective outcomes of pregnancies with paternal periconceptional ustekinumab exposure (n = 87) included 92% live births (1.2% major CA), 5.7% spontaneous abortions and 2.3% elective/induced abortions. CONCLUSIONS: Rates of adverse pregnancy outcomes or CAs with ustekinumab exposure were consistent with rates reported for the US general population and do not suggest a higher risk associated with maternal or paternal exposure to ustekinumab.

Risk Management Plans: reassessment of safety concerns based on Good Pharmacovigilance Practices Module V (Revision 2)-a company experience.

INTRODUCTION: In the European Union (EU), a Risk Management Plan (RMP) is submitted as part of the dossier for initial marketing authorization of a medicinal product or with an application involving a significant change to an existing marketing authorization. A comprehensive revision of the EU Guideline on Good Pharmacovigilance Practices (GVP) Module V-Risk Management Systems (Revision [Rev] 2), adopted in March 2017, provides a framework for developing more focused, actionable, and risk-proportionate RMPs. This paper describes the Janssen experience with the interpretation and application of GVP Module V (Rev 2) regarding the evaluation of safety concerns in an RMP. METHODS: Janssen convened a cross-functional working group to promote consistent interpretation of the GVP Module V (Rev 2) guidance across therapeutic areas. The group created 3 algorithms to support implementation of the guidance related to removal or reclassification of safety concerns by product-specific RMP teams. RESULTS: Following implementation of the GVP Module V (Rev 2) guidance, the algorithm-driven process led to a substantial decrease in the number of safety concerns for most products. With few exceptions, EU health authorities agreed with the proposed safety concern removals or reclassifications, resulting in RMPs that were focused on only those safety concerns that required further characterization or specific risk minimization. CONCLUSIONS: The algorithm-driven process allows for consistent interpretation and application of the GVP Module V (Rev 2) guidance, which enables product teams to develop an actionable RMP using a thoughtful, evaluative, science-based approach that considers all available evidence.

Post-approval Safety Surveillance Study of Golimumab in the Treatment of Rheumatic Disease Using a United States Healthcare Claims Database.

BACKGROUND AND OBJECTIVE: Golimumab is a fully human anti-tumor necrosis factor monoclonal antibody approved for the treatment of rheumatoid arthritis (RA), psoriatic arthritis (PsA), and ankylosing spondylitis (AS). This study estimated rates of prespecified outcomes in patients with RA, PsA or AS initiating golimumab versus matched patients initiating non-biologic systemic (NBS) medications. METHODS: Patients enrolled in a US health plan with rheumatic disease who initiated a study medication were accrued between April 2009 and November 2014. Golimumab initiators were matched by propensity score to NBS initiators in a 1:4 ratio. Outcomes were identified through September 2015. As-treated, as-matched, and nested case-control (NCC) analyses were conducted in the matched cohorts. Sensitivity analyses evaluated the impact of residual confounding and nondifferential misclassification of exposure and outcomes. RESULTS: Risks of outcomes were similar between golimumab and NBS initiators. In the as-treated analysis, the rate ratio (RR) for depression was elevated during current golimumab use versus golimumab non-use in the NBS cohort [RR 1.45, 95% confidence interval (CI) 1.31-1.61]. This finding was not replicated in as-matched (RR 1.08, 95% CI 0.97-1.19) or NCC (odds ratio 1.01, 95% CI 0.78-1.31) analyses, which focused on incident cases. Sensitivity analyses suggest that depression was sensitive to misclassification, and the RR changed from greater than to less than one across a plausible range of specificity. CONCLUSIONS: This study suggests that there is no association between exposure to golimumab and an increased risk of prespecified outcomes. Increased depression risk in the as-treated analysis was not replicated in other analyses and may be associated with residual imbalance in baseline history or severity of depression.

Exposure to Infliximab During Pregnancy: Post-Marketing Experience.

BACKGROUND: Women of childbearing potential are often treated with monoclonal antibodies to control chronic and debilitating inflammatory diseases. Remicade® (innovator infliximab [IFX]) may cross the placenta after the first trimester of pregnancy. Hence, evidence is needed to optimize treatment while carefully weighing benefits and risks to the mother and child. Here, we report on birth and infant outcomes (up to 2 years) following gestational exposure to IFX based on a summary of cumulative pregnancy reports in women exposed to IFX during pregnancy from the Janssen global safety database. METHODS: Prospective and medically confirmed safety data on IFX-exposed pregnancies from Janssen's global safety surveillance database since authorization in 1998 are summarized. Descriptive statistics were used to summarize pregnancy and infant outcomes overall, by disease and timing of exposure. RESULTS: As of 23 August 2018, 1850 maternally IFX-exposed pregnancies with known outcomes were identified from the safety database. Of the 1850 pregnancies (mean age 29.7 years), 1526 (82.5%) resulted in live births. When reported, most women had Crohn's disease (67.7%) or ulcerative colitis (18.4%), and 82.8% of live births were exposed to IFX in the first trimester. Spontaneous abortion/intrauterine death/ectopic pregnancy/molar pregnancy (12.1%), preterm births (9.2%), low birth weight infants (3.6%), congenital anomalies (2.0%), and infant infections (1.2%) were documented. The type of congenital anomalies and frequency of serious infant infections observed were consistent with the general population. Frequencies of congenital anomalies and other adverse outcomes were similar in women exposed to IFX in the first trimester and those exposed in the third trimester. More preterm births (13-18.8%) and infant complications (8.7-12.5%) were reported with concomitant immunosuppressant use. CONCLUSIONS: The observed prevalence of adverse pregnancy and infant outcomes including congenital anomalies following exposure to IFX did not exceed estimates reported for the general population and no unexpected patterns were observed.

Remicade® (infliximab): 20 years of contributions to science and medicine.

On August 24, 1998, Remicade® (infliximab), the first tumor necrosis factor-α (TNF) inhibitor, received its initial marketing approval from the US Food and Drug Administration for the treatment of Crohn's disease. Subsequently, Remicade was approved in another five adult and two pediatric indications both in the USA and across the globe. In the 20 years since this first approval, Remicade has made several important contributions to the advancement of science and medicine: 1) clinical trials with Remicade established the proof of concept that targeted therapy can be effective in immune-mediated inflammatory diseases; 2) as the first monoclonal antibody approved for use in a chronic condition, Remicade helped in identifying methods of administering large, foreign proteins repeatedly while limiting the body's immune response to them; 3) the need to establish Remicade's safety profile required developing new methods and setting new standards for postmarketing safety studies, specifically in the real-world setting, in terms of approach, size, and duration of follow-up; 4) the study of Remicade has improved our understanding of TNF's role in the immune system, as well as our understanding of the pathophysiology of a range of diseases characterized by chronic inflammation; and 5) Remicade and other TNF inhibitors have transformed treatment practices in these chronic inflammatory diseases: remission has become a realistic goal of therapy and long-term disability resulting from structural damage can be prevented. This paper reviews how, over the course of its development and 20 years of use in clinical practice, Remicade was able to make these contributions.

Effectiveness of the golimumab educational program in ensuring healthcare professionals' awareness of risks described in the European risk management plan.

BACKGROUND: The golimumab safety awareness study commenced in 2010 to measure, periodically, the awareness of golimumab prescriber healthcare professionals (HCPs) of specific risks associated with golimumab as well as awareness of the requirement to provide a patient alert card to each patient treated with golimumab, as described in the European golimumab educational program. The aim of this study was to measure the awareness of HCPs who prescribe or who intend to prescribe SIMPONI® (golimumab) of the risks potentially related to golimumab and of the requirements for distributing the patient alert card, as described in the golimumab educational program. METHODS: A structured, quantitative Web-based survey was conducted in 2010, 2012, 2014, and 2016 in eight European countries among HCPs who were at that time current or future prescribers of golimumab for patients with rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, nonradiographic axial spondyloarthritis, or ulcerative colitis. RESULTS: The overall golimumab risk awareness was high for golimumab prescriber HCPs across the risk statement categories (median awareness in 2016 across categories: 91%). The awareness of the golimumab risks was generally slightly higher among rheumatologists (75-98%) and gastroenterologists (73-97%) than among dermatologists (67-94%). Overall, the awareness of the requirements for handing out the patient alert card to golimumab-treated patients remained steady or increased slightly in 2016 relative to the other surveys. CONCLUSIONS: The results of this study show that the awareness of risks associated with golimumab by golimumab prescriber HCPs is high. The information made available to golimumab prescriber HCPs appears to have been sufficient with respect to golimumab risk awareness education.

Four-year follow-up of infliximab therapy in rheumatoid arthritis patients with long-standing refractory disease: attrition and long-term evolution of disease activity.

Although there is strong evidence supporting the short-term efficacy and safety of anti-tumour necrosis factor-alpha agents, few studies have examined the long-term effects. We evaluated 511 patients with long-standing refractory rheumatoid arthritis treated with intravenous infusions of infliximab 3 mg/kg at weeks 0, 2, 6, and 14 and every 8 weeks thereafter for 4 years. Among the initial 511 patients included in the study, 479 could be evaluated; of these, 295 (61.6%) were still receiving infliximab treatment at year 4 of follow-up. The most common reasons for treatment discontinuation were lack of efficacy (65 patients, 13.6%), safety (81 patients, 16.9%), and elective change (38 patients, 7.9%). Analysis of disease activity scores (DAS28 [disease activity score based on the 28-joint count]) over time showed that, after the initial rapid improvement during the first 6 to 22 weeks of therapy, a further decrease in disease activity of 0.2 units in the DAS28 score per year was observed. DAS28 scores, measured at week 14 or 22, were found to predict subsequent discontinuation due to lack of efficacy. In conclusion, long-term maintenance therapy with infliximab 3 mg/kg is effective in producing further reductions in disease activity. Disease activity measured by the DAS28 at week 14 or 22 of infliximab therapy was the best predictor of long-term attrition.

DAS28 best reflects the physician's clinical judgment of response to infliximab therapy in rheumatoid arthritis patients: validation of the DAS28 score in patients under infliximab treatment.

This study is based on an expanded access program in which 511 patients suffering from active refractory rheumatoid arthritis (RA) were treated with intravenous infusions of infliximab (3 mg/kg+methotrexate (MTX)) at weeks 0, 2, 6 and every 8 weeks thereafter. At week 22, 474 patients were still in follow-up, of whom 102 (21.5%), who were not optimally responding to treatment, received a dose increase from week 30 onward. We aimed to build a model to discriminate the decision to give a dose increase. This decision was based on the treating rheumatologist's clinical judgment and therefore can be considered as a clinical measure of insufficient response. Different single and composite measures at weeks 0, 6, 14 and 22, and their differences over time were taken into account for the model building. Ranking of the continuous variables based on areas under the curve of receiver-operating characteristic (ROC) curve analysis, displayed the momentary DAS28 (Disease Activity Score including a 28-joint count) as the most important discriminating variable. Subsequently, we proved that the response scores and the changes over time were less important than the momentary evaluations to discriminate the physician's decision. The final model we thus obtained was a model with only slightly better discriminative characteristics than the DAS28. Finally, we fitted a discriminant function using the single variables of the DAS28. This displayed similar scores and coefficients as the DAS28. In conclusion, we evaluated different variables and models to discriminate the treating rheumatologist's decision to increase the dose of infliximab (+MTX), which indicates an insufficient response to infliximab at 3 mg/kg in patients with RA. We proved that the momentary DAS28 score correlates best with this decision and demonstrated the robustness of the score and the coefficients of the DAS28 in a cohort of RA patients under infliximab therapy.

Pattern recognition receptors and differentiation antigens define murine myeloid cell heterogeneity ex vivo.

Recruitment of myeloid cells during inflammatory reactions plays an important role in the propagation and resolution of inflammation. However, the identification and characterization of these cells in mice has been hampered by cellular heterogeneity at the functional and phenotypic level. We have defined criteria for the rapid flow-cytometric identification of monocytes (M(o)), macrophages (MPhi), neutrophils (N(eu)) and eosinophils (E(os)) in murine tissues using novel and established myeloid markers. These criteria were applied to the study of naive mice and mice with experimentally induced inflammation, both local and systemic, and also to a murine model of tumor progression. We show that the murine 7/4 antigen and the beta-glucan receptor, Dectin-1, are particularly useful for the sub-division of myeloid cells into individual populations, even when inflammatory conditions modulate their surface expression. Furthermore, 7/4 expression allows distinction between M(o) recently recruited to a site and the resident cells already present. These studies highlight the heterogeneity of the murine M(o)/MPhi-lineage, define an extended phenotype for murine myeloid cells and greatly facilitate the ex vivo characterization of these cells during very different models of inflammation.

Morphometric analysis of cytolysis in cultured cell monolayers: a simple and versatile method for the evaluation of the lytic activity and the fate of LAK cells.

The assessment of cytolytic activity of killer cells may not only be useful to improve routine analysis, e.g., in clinical settings, but may also offer new opportunities for the fundamental analysis of the mutual interaction between cytotoxic cells and their targets. We have developed a morphometric method to estimate cytolytic activity of activated natural killer (NK) cells by measuring the clearance of a precultured confluent monolayer of adherent target cells, e.g., immortalized fibroblasts. Cytotoxic cells are inoculated on top of confluent monolayers of target cells and after 2 h, nonadherent cells are washed off and intact adherent cells are fixed and stained with a Coomassie blue solution. Elementary computer-assisted analysis of the resulting microscopic images and measurement of the cleared area provide us with a sensitive and reproducible parameter of target cell lysis. We found that the assay can be used with targets of very different origin, as long as they form confluent monolayers, and with different populations of killer cells. The morphometric cytotoxicity assay (MoCA) offers several advantages: storage of samples for postponed analysis, increased sensitivity as compared to radioactive assays, continuous visualization during assay, availability of targets and effectors for subsequent analysis after interaction.

Nitric oxide-independent CTL suppression during tumor progression: association with arginase-producing (M2) myeloid cells.

Most of the mice bearing a s.c. BW-Sp3 lymphoma tumor mount a CD8(+) T cell-mediated response resulting in tumor regression. Nonetheless, tumor progression occurs in some of the recipients and is associated with CTL inactivity. We demonstrated that T cell-activating APC were induced in regressors whereas T cell suppressive myeloid cells predominated in the spleen of progressors. Indeed, in vitro depletion of either the adherent or the CD11b(+) populations restored T cell cytotoxicity and proliferation in these mice. This CTL inhibition was cell-to-cell contact-dependent but not mediated by NO. However, the same progressor suppressive cells prevented the activity of in vitro-restimulated CTLs derived from regressors in a cell-to-cell contact and NO-dependent fashion. Thus, either the NO-dependent or -independent suppressive pathway prevailed, depending on the target CTL population. In addition, the suppressive population expressed a high arginase activity, suggesting an association of the suppressive phenotype with alternatively activated (M2) myeloid cells. However, the high arginase activity is not directly involved in the suppressive process. Our results provide new insights for myeloid cell-mediated CTL inhibition during cancer progression.

Ablation of NK cell function during tumor growth favors Type 2-associated macrophages, leading to suppressed CTL generation.

Several reports describe regulatory interactions between NK cells and CTLs. We addressed the issue of NK participation in the early anti-tumor defense by inoculating alpha-ASGM-1 treated mice with BW-Sp3 T lymphoma. Rejection of BW-Sp3 depends on strong CTL responses. Our results demonstrated that (i) NK cells are a prerequisite for efficient CTL generation and (ii) the absence of NK cells favors the outgrowth of alternatively activated macrophages that can suppress CTL restimulation. In vitro studies demonstrate that in splenic cultures from NK-deficient, tumor-bearing mice, the presence of alternatively activated macrophages correlates with a lack of Type 1 cytokines, while the production of Type 2 cytokines is promoted. Provision of the Type 1 cytokine, IFN-gamma can boost overall CTL activity but does not revert the dominance of arginase producing adherent cells in the NK-deficient CTL cultures. The role of NK effector functions in the efficient switch of the immune system towards Type 1 activation was evaluated in cytotoxicity assays. The results indicate that the accessory function of NK can depend at least partially on their ability to preferentially engage arginase-producing cells, suggesting that NK/macrophage lytic interactions might be involved in the switch from Type 2 to Type 1-dependent immune responses.

Antagonistic effect of NK cells on alternatively activated monocytes: a contribution of NK cells to CTL generation.

Natural killer (NK) cells fulfill essential accessory functions for the priming of antigen-specific cytotoxic T lymphocytes (CTLs). On the basis of a NKG2D-ligand-positive tumor model, we obtained results implicating NK-mediated regulatory as well as NK-mediated cytolytic activities in the initiation and persistence of CTL activity. Indeed, CD8(+) T-cell-dependent tumor rejection requires NK cell function in vivo, because tumors will progress both on depletion of NK cells or in the absence of optimal NK activity. Here we provide evidence that the absence of NK cells during subcutaneous tumor growth will abrogate generation of antitumor CTL responses and that this process can be linked to the expansion of alternatively activated monocytes. Indeed, our in vitro studies demonstrate that in splenic cultures from NK-deficient tumor-bearing mice, lack of type 1-associated cytokines correlates with the presence of type 2 (alternatively activated) monocytes and the production of type 2 cytokines. Furthermore, these type 2 monocyte-containing splenic adherent populations potently suppress subsequent memory CTL restimulation. We evaluated the role of NK lytic effector functions in the efficient switch of the immune system toward classical (type 1) activation by including differentially activated monocytic populations as targets in cytotoxicity assays. The results indicate that the accessory function of NK cells depends partially on the ability of activated NK cells to preferentially engage type 2 antigen-presenting cells. Thus, when the immune system tends to be type 2 oriented, NK cells can drive an efficient type 2 --> type 1 switch in the population of antigen-presenting cells to provide signaling for the generation of CTLs.

Morphometric analysis of cytolysis in cultured cell monolayers: a simple and versatile method for the evaluation of the cytotoxic activity and the fate of LAK cells.

In vitro techniques for the evaluation of the cytotoxicity of immune cells are important both for the routine assessment of the cytolytic activity in samples for clinical or experimental use and for basic studies of the interaction between killer and target cells. Especially in the latter case, it is important not only to quantify target cell death as an endpoint, but also to observe the interaction and to recover effectors and targets for further analysis. We present a new method that offers considerable improvements for both types of applications, in comparison with the standard radioactivity release assays used today. The morphometric cytotoxicity assay (Mo.C.A.) estimates the extent of target cell lysis by measuring the openings that appear in a confluent monolayer of adherent cells as killed cells detach from the plastic on which they were spread. Two hours after the inoculation of the effector cells, nonadherent killer and dead target cells are washed off and the remaining monolayer is fixed and stained with Coomassie blue. Elementary computer-assisted image analysis allows then to calculate the percentage of open space, which is a parameter for the extent of lysis. As the Mo.C.A. is easy, and does not rely on the use of radioactive compounds or sophisticated equipment, we provide evidence that it should be valuable for the routine analysis of cytotoxicity in various cell samples. In addition, the method offers great flexibility in the choice of target cells and allows for continuous microscopic observation of the live cultures. The interaction can also be stopped at any time, and the effector and (unlabeled) target cells can be recovered separately. Therefore, the method should also offer new possibilities for the basic study of killer cell biology.