Abstract 5586: Demonstrating restoration of T cell function in exhausted T cells with IKZF3 small molecule inhibitor, Lenalidomide

CD8+ T cell exhaustion as a result of prolonged antigenic stimulation in the tumour microenvironment is thought to be a major mechanism by which tumours can escape immune surveillance. T cell exhaustion is characterised by co-expression of checkpoint inhibitor molecules such as PD-1, LAG-3 and TIM-3; reduced proliferative capacity; and diminished production of pro-inflammatory cytokines such as IL-2, IFN-γ and TNF-α and treatment with checkpoint inhibitor blockade such as Nivolumab (anti-PD-1) have shown great promise in the treatment of a subset of individuals and tumour types. However, resistance to these approaches is prevalent and there is a need to identify novel targets to provide alternative options for the rescue of T cell exhaustion and cancer treatment for use alone or potentially in combination with checkpoint inhibitor modulation. One such target is IKZF3, a transcription factor that is increased in murine models of T cell exhaustion and reduces IL-2 expression. Previously we presented an in vitro human T cell exhaustion assay whereby in vitro stimulated T cells phenotypically and functionally recapitulate the exhausted T cells found within the tumour microenvironment and now we demonstrate that exhaustion can be partially rescued by treatment with the IKZF3 small molecule inhibitor, Lenalidomide, alone and in combination with checkpoint inhibitor blockade. The use of small molecule inhibitors offers new avenues for reversing T cell exhaustion in cases of checkpoint inhibitor resistance and this platform delivers a robust assay allowing for assessment of small molecules or checkpoint inhibitors both individually and in combination.

Citation Format: Joanne Hay, Francis Acklam, Darryl Turner, Mark Barbour, Preeti Singh, Courtney Grant, Hayley Gooding, Rhoanne McPherson, Justyna Rzepecka. Demonstrating restoration of T cell function in exhausted T cells with IKZF3 small molecule inhibitor, Lenalidomide [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5586.

Anti-CD52 antibody treatment in murine experimental autoimmune encephalomyelitis induces dynamic and differential modulation of innate immune cells in peripheral immune and central nervous systems

Anti‐CD52 antibody (anti‐CD52‐Ab) leads to a rapid depletion of T and B cells, followed by reconstitution of immune cells with tolerogenic characteristics. However, very little is known about its effect on innate immune cells. In this study, experimental autoimmune encephalomyelitis mice were administered murine anti‐CD52‐Ab to investigate its effect on dendritic cells and monocytes/macrophages in the periphery lymphoid organs and the central nervous system (CNS). Our data show that blood and splenic innate immune cells exhibited significantly increased expression of MHC‐II and costimulatory molecules, which was associated with increased capacity of activating antigen‐specific T cells, at first day but not three weeks after five daily treatment with anti‐CD52‐Ab in comparison with controls. In contrast to the periphery, microglia and infiltrating macrophages in the CNS exhibited reduced expression levels of MHC‐II and costimulatory molecules after antibody treatment at both time‐points investigated when compared to controls. Furthermore, the transit response of peripheral innate immune cells to anti‐CD52‐Ab treatment was also observed in the lymphocyte‐deficient SCID mice, suggesting the changes are not a direct consequence of the mass depletion of lymphocytes in the periphery. Our study demonstrates a dynamic and tissue‐specific modulation of the innate immune cells in their phenotype and function following the antibody treatment. The findings of differential modulation of the microglia and infiltrating macrophages in the CNS in comparison with the innate immune cells in the peripheral organs support the CNS‐specific beneficial effect of alemtuzumab treatment on inhibiting neuroinflammation in multiple sclerosis patients.

251 The use of small molecule inhibitors to target novel pathways in exhausted T cells for immuno-oncology therapeutic intervention

Background

The ability to reverse exhaustion in CD8+ T cells holds great promise for therapeutic intervention in oncology. Indeed, treatment with therapeutics targeted at checkpoint inhibitors, such as Nivolumab (anti-PD-1), have shown great promise in the treatment of a subset of individuals and tumour types. However, pre-clinical success does not always translate to success in clinical trials and resistance to these approaches is prevalent. As such, there is a pressing need to develop novel approaches that target alternative pathways for use alone or potentially in combination with checkpoint inhibitor modulation. A secondary need is the requirement for advanced assays that accurately recapitulate the pathways and cell phenotypes prevalent in the tumour environment.

Methods

Here we describe the characteristics of an in vitro human T cell exhaustion assay whereby in vitro stimulated T cells phenotypically and functionally recapitulate the exhausted T cells found within the tumour microenvironment. We also demonstrate the effect of checkpoint blockade as well as small molecule inhibition of a novel target on the exhausted T cell phenotype.

Results

In this assay, exhaustion can be partially but not fully reversed by treatment with anti-PD-1 alone. In addition, we demonstrate the effect of a small molecule inhibitor targeting IKZF3, a transcription factor shown to be upregulated in T cell exhaustion, on reversing T cell exhaustion alone and in combination with checkpoint inhibitor blockade.

Conclusions

These assays and approaches enable investigation into the ability of compounds to influence reversal of T cell exhaustion where anti-PD-1 treatment does not fully reverse the exhausted phenotype and offers the ability to test combination therapy approaches.

Acknowledgements

This work was aided by the valuable input and insight of Professor Stephen Anderton.

Ethics Approval

The study obtained ethics approval from West Midlands – Black Country Research Ethics Committee under IRAS project ID 270936. All donors gave informed consent before taking part.

The impact of anxiety level on medical decisions of non-COVID patients during the pandemic outbreak

Background

High anxiety levels (HAL) were widely reported in patients during the COVID outbreak. We assess whether HAL influenced medical decision-making (MDM) of Non-COVID patients.

Method

We prospectively recruited patients with cardiovascular complaints during February and September 2020. We assessed anxiety levels using the GAD-7, Beck Inventory, the cardiac anxiety questionnaires, and a newly designed MDM questionnaire.

Results

We recruit 287 patients. The mean age was 52.6±14.9 (females represent 36.2%). HAL was reported in 261 (90.3) patients and was more prevalent in old (p<0.001 for all questionnaires), married, and unemployed patients (significant p-value for all). Cardiovascular comorbidities and a history of anxiety, depression, and psychiatric disorder were independent factors for HAL (p<0.001 for all). Coronary catheterization was performed more in HAL (p<0.001 for all), yet the rate of significant coronary artery disease was lower than in patients with low anxiety level (LAL) (p<0.001 for all). 161 (56.9) patients reported that their MDM was affected (<0.001), and 149 (76.8) patients indicated that they would have gone earlier to the hospital if not the pandemic (p=0.03 for high DM-19 score). Patients with HAL seek medical care longer than LAL patients (p=0.02). Correlation analysis revealed a positive correlation between MDM and HAL (p<0.001 for all).

Conclusion

Our study shows a strong and positive correlation between anxiety level and MDM. Old patients with cardiovascular comorbidities and a history of mental disorders were at particularly high risk for HAL and sought medical treatment significantly longer than LAL patients.

Funding Acknowledgement

Type of funding sources: None.

Abstract LB158: Implications of Targeting Novel Pathways in Exhausted T Cells for Immuno-Oncology Therapeutic Intervention

The induction of CD8+ T cell exhaustion, driven by the tumor microenvironment, is thought to be a major mechanism by which tumors can escape immune surveillance and are able to persist and progress. T cell exhaustion is typically characterized by the expression of co-inhibitory markers such as PD-1, LAG-3 and TIM-3 and a reduced capacity for pro-inflammatory cytokine production. Whilst treatment with therapeutics targeted at checkpoint inhibitors, such as Nivolumab (anti-PD-1), have shown great promise in the treatment of a subset of individuals and tumor types, resistance to these approaches is prevalent. As such, novel approaches are required in order to provide alternative options for the rescue of T cell exhaustion and cancer treatment.

Here we describe the characteristics of an in vitro human T cell exhaustion assay whereby in vitro stimulated T cells phenotypically and functionally recapitulate the exhausted T cells found within the tumor microenvironment and where exhaustion can be partially rescued by treatment with anti-PD-1. Furthermore, we demonstrate the effect of treatment with an inhibitor of a novel target identified in exhausted T cells on T cell function; both through analysis of pro-inflammatory cytokine production and the ability to kill tumor cells. These assays and approaches enable investigation into the ability of compounds to influence reversal of T cell exhaustion where anti-PD-1 treatment does not fully reverse the exhausted phenotype and offers the ability to test combination therapy approaches.

Citation Format: Rhoanne McPherson, Francis Acklam, Joanne Hay, Mark Barbour, Courtney Grant, Preeti Singh, Adriana Gambardella, Justyna Rzepecka, Stephen Anderton, Hayley Gooding. Implications of Targeting Novel Pathways in Exhausted T Cells for Immuno-Oncology Therapeutic Intervention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB158.

Petrifilm™ Rapid S. aureus Count Plate Method for Rapid Enumeration of Staphylococcus aureus in Selected Foods: Collaborative Study

A rehydratable dry-film plating method for Staphylococcus aureusin foods, the 3M™ Petrifilm™ Rapid S. aureus Count Plate method, was compared with AOAC® Official MethodSM 975.55 (Staphylococcus aureus in Foods). Nine foods—instant nonfat dried milk, dry seasoned vegetable coating, frozen hash browns, frozen cooked chicken patty, frozen ground raw pork, shredded cheddar cheese, fresh green beans, pasta filled with beef and cheese, and egg custard—were analyzed for S. aureus by 13 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample and 3 levels of inoculated test sample, each in duplicate. The mean log counts for the methods were comparable for pasta filled with beef and cheese; frozen hash browns; cooked chicken patty; egg custard; frozen ground raw pork; and instant nonfat dried milk. The repeatability and reproducibility variances of the Petrifilm Rapid S. aureus Count Plate method were similar to those of the standard method.

Role of IL-33/ST2 signaling pathway in systemic sclerosis and other fibrotic diseases

Systemic sclerosis (SSc) is a complex autoimmune disease characterised by fibrosis of the skin and multiple internal organs. Interleukin 33 (IL-33) has recently been investigated as a potential key player in the pathogenesis of SSc and other fibrotic diseases, owing to its effects on tissue fibrosis. Understanding how IL-33 is regulated and how it contributes to the development of fibrosis will be important to elucidate disease pathogenesis and may shed light on new areas for therapeutic development for patients. Here we discuss the recent research progress in our understanding of the role and the underlying mechanisms of IL-33/ST2 signaling pathway in SSc and other fibrotic diseases.

Expression and Function of IL-33/ST2 Axis in the Central Nervous System Under Normal and Diseased Conditions

Interleukin-33 (IL-33) is a well-recognized immunomodulatory cytokine which plays critical roles in tissue function and immune-mediated diseases. The abundant expression of IL-33 in brain and spinal cord prompted many scientists to explore its unique role in the central nervous system (CNS) under physiological and pathological conditions. Indeed emerging evidence from over a decade's research suggests that IL-33 acts as one of the key molecular signaling cues coordinating the network between the immune and CNS systems, particularly during the development of neurological diseases. Here, we highlight the recent advances in our knowledge regarding the distribution and cellular localization of IL-33 and its receptor ST2 in specific CNS regions, and more importantly the key roles IL-33/ST2 signaling pathway play in CNS function under normal and diseased conditions.

The therapeutic effect of anti-CD52 treatment in murine experimental autoimmune encephalomyelitis is associated with altered IL-33 and ST2 expression levels

Experimental autoimmune encephalomyelitis (EAE) mice were administered with murine anti-CD52 antibody to investigate its therapeutic effect and whether the treatment modulates IL-33 and ST2 expression. EAE severity and central nervous system (CNS) inflammation were reduced following the treatment, which was accompanied by peripheral T and B lymphocyte depletion and reduced production of various cytokines including IL-33, while sST2 was increased. In spinal cords of EAE mice, while the number of IL-33⁺ cells remained unchanged, the extracellular level of IL-33 protein was significantly reduced in anti-CD52 antibody treated mice compared with controls. Furthermore the number of ST2⁺ cells in the spinal cord of treated EAE mice was downregulated due to decreased inflammation and immune cell infiltration in the CNS. These results suggest that treatment with anti-CD52 antibody differentially alters expression of IL-33 and ST2, both systemically and within the CNS, which may indicate IL-33/ST2 axis is involved in the action of the antibody in inhibiting EAE.

Effect of sphingosine kinase modulators on interleukin-1β release, sphingosine 1-phosphate receptor 1 expression and experimental autoimmune encephalomyelitis

BACKGROUND AND PURPOSE

The sphingosine analogue, FTY720 (GilenyaR ), alleviates clinical disease progression in multiple sclerosis. Here, we variously assessed the effects of an azide analogue of (S)-FTY720 vinylphosphonate (compound 5; a sphingosine kinase 1 activator), (R)-FTY720 methyl ether (ROMe, a sphingosine kinase 2 inhibitor) and RB-020 (a sphingosine kinase 1 inhibitor and sphingosine kinase 2 substrate) on IL-1β formation, sphingosine 1-phosphate levels and expression of S1P1 receptors. We also assessed the effect of compound 5 and ROMe in an experimental autoimmune encephalomyelitis (EAE) model in mice.

EXPERIMENTAL APPROACH

We measured IL-1β formation by macrophages, sphingosine 1-phosphate levels and expression levels of S1P1 receptors in vitro and clinical score in mice with EAE and the extent of inflammatory cell infiltration into the spinal cord in vivo.

KEY RESULTS

Treatment of differentiated U937 macrophages with compound 5, RB-020 or sphingosine (but not ROMe) enhanced IL-1β release. These data suggest that these compounds might be pro-inflammatory in vitro. However, compound 5 or ROMe reduced disease progression and infiltration of inflammatory cells into the spinal cord in EAE, and ROMe induced a reduction in CD4+ and CD8+ T-cell levels in the blood (lymphopenia). Indeed, ROMe induced a marked decrease in expression of cell surface S1P1 receptors in vitro.

CONCLUSION AND IMPLICATIONS

This is the first demonstration that an activator of sphingosine kinase 1 (compound 5) and an inhibitor of sphingosine kinase 2 (ROMe, which also reduces cell surface S1P1 receptor expression) have an anti-inflammatory action in EAE.

Interleukin-33 predicts poor prognosis and promotes ovarian cancer cell growth and metastasis through regulating ERK and JNK signaling pathways

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer, it remains a huge challenge to understand the cellular and molecular mechanisms of the aggressive behavior of EOC cells. Here we investigated the role of an immunomodulatory cytokine IL-33 and its receptor ST2 in mediating the growth and metastasis of EOC. Our data show that both IL-33 and ST2 were highly up-regulated in EOC tumors compared with normal ovary and ovarian benign tumors, and the expression levels were further increased in tumor tissues at the metastatic site. The expression levels of IL-33 and ST2 were positively correlated with the Ki-67 expression, and negatively correlated with the patient survival time. Using EOC cell lines, we observed that cells knocked down of IL-33 gene by siRNA had reduced migratory and invasive potential, while full length human IL-33 (fl-hIL-33) promoted the invasive, migratory and proliferative capacity of EOC cells and this process could be inhibited by IL-33 decoy receptor sST2. Signaling pathway analysis suggested that IL-33 increased the phosphorylation of ERK and JNK which was blocked by sST2. Fl-hIL-33-induced increases in EOC cell migration, invasive potential and proliferation were specifically abrogated by treatment with the ERK inhibitor U0126 while JNK inhibitor SP600125 only disrupted IL-33-induced enhancement of cell viability. Taken together, our data suggest that IL-33/ST2 axis closely associates with poor prognosis of EOC patients, and it promotes ovarian cancer growth and metastasis through regulating ERK and JNK signaling pathways. Thus IL-33/ST2 might be potential prognosis markers and therapeutic targets for EOC patients.

IL-33 attenuates the development of experimental autoimmune uveitis

Interleukin-33 (IL-33) is associated with several important immune-mediated disorders. However, its role in uveitis, an important eye inflammatory disease, is unknown. Here, we investigated the function of IL-33 in the development of experimental autoimmune uveitis (EAU). IL-33 and IL-33 receptor (ST2) were expressed in murine retinal pigment epithelial (RPE) cells in culture, and IL-33 increased the expression of Il33 and Mcp1 mRNA in RPE cells. In situ, IL-33 was highly expressed in the inner nuclear cells of the retina of naïve mice, and its expression was elevated in EAU mice. ST2-deficient mice developed exacerbated EAU compared with WT mice, and administration of IL-33 to WT mice significantly reduced EAU severity. The attenuated EAU in IL-33-treated mice was accompanied by decreased frequency of IFN-γ+ and IL-17(+) CD4+ T cells and reduced IFN-γ and IL-17 production but with increased frequency of IL-5(+) and IL-4(+) CD4 T cells and IL-5 production in the draining lymph node and spleen. Macrophages from the IL-33-treated mice show a significantly higher polarization toward an alternatively activated macrophage phenotype. Our results therefore demonstrate that the endogenous IL-33/ST2 pathway plays an important role in EAU, and suggest that IL-33 represents a potential option for treatment of uveitis.

Emerging role of interleukin-33 in autoimmune diseases

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family. It predominantly induces type 2 immune responses and thus is protective against atherosclerosis and nematode infections but contributes to allergic airway inflammation. Interleukin-33 also plays a pivotal role in the development of many autoimmune diseases through mechanisms that are still not fully understood. In this review, we focus on the recent advances in understanding of the expression and function of IL-33 in some autoimmune disorders, aiming to provide insight into its potential role in disease development.

Varicella-zoster virus gene 21: transcriptional start site and promoter region

Varicella-zoster virus (VZV) causes chicken pox (varicella), becomes latent in dorsal root ganglia, and reactivates decades later to cause shingles (zoster). During latency, the entire VZV genome is present in a circular form, from which genes 21, 29, 62, and 63 are transcribed. Immediate-early (IE) VZV genes 62 and 63 encode regulators of virus gene transcription, and VZV gene 29 encodes a major DNA-binding protein. However, little is known about the function of VZV gene 21 or the control of its transcription. Using primer extensions, we mapped the start of VZV gene 21 transcription in VZV-infected cells to a single site located at -79 nucleotides (nt) with respect to the initiation codon. To identify the VZV gene 21 promoter, the 284-bp region of VZV DNA separating open reading frames (ORFs) 20 and 21 was cloned upstream from the chloramphenicol acetyltransferase gene. In transient-transfection assays, the VZV gene 21 promoter was transactivated in VZV-infected, but not uninfected, cells. Further, the protein encoded by ORF 62 (IE62), but not those encoded by VZV ORFs 4, 10, 61, and 63, transactivates the VZV gene 21 promoter. By use of transient-cotransfection assays in conjunction with 5' deletions of the VZV gene 21 promoter, a 40-bp segment was shown to be responsible for the transactivation of the VZV gene 21 promoter by IE62. This region was located at -96 to -56 nt with respect to the 5' start of gene 21 transcription.

An homogeneous fluorescence polymerase chain reaction assay to identify Salmonella

We have developed a semiquantitative homogeneous fluorescence assay that combines polymerase chain reaction (PCR) amplification with direct fluorescence detection (HF-PCR). The assay eliminates the need to perform gel electrophoresis on test samples. Using a set of Salmonella-specific primers, this system was used to verify suspect colonies from culture plates as Salmonella. The fluorescence signal is generated by a nucleic acid dye, YO-PRO-1, that is included in the amplification reaction. This homogeneous PCR assay was used to test 84 Salmonella strains picked from selective culture plates. All data indicated positive results when compared with 17 non-Salmonella strains (in general, Citrobacter, Hafnia, Proteus, and Escherichia). The HF-PCR assay is a sensitive, simple, accurate, and reproducible method that correlates well with size-exclusion high-performance liquid chromatography and gel electrophoresis techniques as a means to monitor PCR-mediated DNA amplification. This assay can confirm suspect colonies within 2.5 h.

Varicella-zoster virus (VZV) transcription during latency in human ganglia: detection of transcripts mapping to genes 21, 29, 62, and 63 in a cDNA library enriched for VZV RNA

Information on the extent of virus DNA transcription and translation in infected tissue is crucial to an understanding of herpesvirus latency. To detect low-abundance latent varicella-zoster virus (VZV) transcripts, poly(A)+ RNA extracted from latently infected human trigeminal ganglia was enriched for VZV transcripts by hybridization to biotinylated VZV DNA. After hybridization, the RNA-DNA hybrid was isolated by binding to avidin-coated beads and extensively washed, and the RNA was released by heat denaturation. A lambda-based cDNA library was then constructed from the enriched RNA. PCR and DNA sequencing of DNA extracted from the cDNA library revealed the presence of VZV genes 21, 29, 62, and 63, but not VZV genes 4, 10, 40, 51, and 61, in the enriched cDNA library. These findings confirm the detection of VZV gene 29 and 62 transcripts on Northern (RNA) blots prepared from latently infected human ganglia (J.L. Meier, R.P. Holman, K.D. Croen, J.E. Smialek, and S.E. Straus, Virology 193:193-200, 1993) and the presence of VZV gene 21 transcripts in a cDNA library from mRNA of latently infected ganglia (R.J. Cohrs, K. Srock, M.B. Barbour, G. Owens, R. Mahalingam, M.E. Devlin, M. Wellish and D.H. Gilden, J. Virol. 68:7900-7908,1994) and also reveal, for the first time, the presence of VZV gene 63 RNA in latently infected human ganglia.

Levels of five mycotoxins in grains harvested in Atlantic Canada as measured by high performance liquid chromatography

An analytical protocol using high performance liquid chromatography (HPLC) was used to analyze samples of spring wheat, winter wheat, 2-row barley, and 6-row barley over a period of three years for the presence of five mycotoxins. These included deoxynivalenol, zearalenone, T-2 toxin, HT-2 toxin, and diacetoxyscirpenol. The protocol employed a single extraction step using acetonitrile-water and two cleanup procedures. One utilized a solid-phase extraction column and the other a charcoal-alumina column. Detection limits ranged from 0.02 to 0.15 micrograms of mycotoxin g-1 grain. Little T-2 toxin, HT-2 toxin, or diacetoxyscirpenol was found in the samples. Deoxynivalenol was detected in 53 to 62% of the samples tested and zearalenone in 25-29% of the samples. Several enzyme-linked immunosorbent assays were used for comparison purposes with deoxynivalenol, zearalenone, and T-2 toxin. These kits provided reliable qualitative, but not quantitative, data.

Evaluation of the use and usefulness of telephone consultations in one general practice

In one practice with 14,000 patients an advice line was set aside at designated times to enable patients to speak directly to a doctor on the telephone. The aim of this study was to determine who used the line, why they called, the conditions callers presented with, the action taken by the doctor and whether patients and doctors thought the service was a good idea. A total of 277 calls were made during the five month study period. Responses to a questionnaire were received from doctors for all 277 calls and from 152 patients. It was found that most calls lasted about three minutes. Most of the callers (59%) were known to the doctor taking the call. Users of the advice line were most likely to be women, married people and people with children. Equal numbers of calls were received about new and existing problems. The most frequent reason for calling was to obtain the result of a test (21% of calls). The most frequent diagnosis by the doctors was chronic complaints for which the patient was already receiving treatment (19%). The data from patients and doctors were similar. In 30% of cases callers were advised to take medicine, mostly a prescription to be collected (16%), while a few callers received a home visit (7%). Doctors thought they provided reassurance in 26% of cases while callers thought they had received reassurance in 43% of cases. If the advice line had not been available three quarters of the respondents would have made an appointment and 13% would have asked the doctor to make a home visit.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term comparison of metoprolol and methyldopa in the treatment of hypertension

The effect of the cardioselective beta-adrenoreceptor blocking compound, metoprolol, was compared with methyldopa in the long-term management of hypertension. Thirty patients given metoprolol and twenty-six given methyldopa were treated for 2 years. The maximum dose of metoprolol was 200 mg twice daily (average 308 mg) and of methyldopa 1,000 mg twice daily (average 1,120 mg). Blood pressure was similar at entry to the study (metoprolol 177/110 mmHg and methyldopa 181/111 mmHg). After 2 years of treatment the blood pressure levels were again similar (metoprolol 149/91 mmHg and methyldopa 148/91 mmHg). Erect pressures were lower in the methyldopa group, but there was no difference between supine and erect blood pressure levels in those on metoprolol. At an exercise load of 300 and 600 kpm the increase in systolic pressure was significantly less in the metoprolol group. The proportional increase in systolic and diastolic pressure in response to a standardized stress situation was reduced by treatment with metroprolol but not by methyldopa. Tolerance to therapy did not develop in either group. The main difference between metoprolol and methyldopa was in the incidence and severity of side effects. Four patients were withdrawn from the metoprolol group. Seventeen were withdrawn from the methyldopa mainly because of side effects including drowsiness, depression, skin rash, and impotence. Six patients on metoprolol and seventeen on methyldopa continued on therapy although side effects were present. It is concluded that metoprolol and methyldopa lower blood pressure to the same extent, but metoprolol is advantageous because of a lower incidence of side effects.