P13.13 Clinical factors involved in brain metastasis edema: results of a retrospective cohort and evaluation of the best edema descriptor

BACKGROUND

Brain metastasis (BM) are frequently surrounded by brain edema with a variable extension. This pathological increase in the water mass from the interstitial or intracellular space is the source of neurological symptoms but some studies also showed a prognosis impact of this edema. Nevertheless, the current edema evaluation methods are poorly reproducible and were not extensively evaluated. From a series of patients with brain metastasis, we analyzed factors influencing perilesional edema extension in function of three edema descriptors which were qualitatively evaluated: the absolute cumulative intracranial edema volume (CIEV, in mL), the edema on tumor volume ratio (ER), and the Edema Theoretical Thickness (ETT, in mm), new factor designed to be more independent from geometrical considerations.

MATERIAL AND METHODS

Clinical, biological and imaging factors were retrospectively recorded from patients referred for upfront stereotactic radiotherapy of one to three BMs. CIEV, ER and ETT were calculated for each patient. Non-colinear factors were selected using the Farrar-Glauber test. Impact of these factors on edema was tested with an univariate then a multivariate linear regression for each edema descriptor. Each resulting regression model was qualitatively evaluated using the F-test, R square value and residuals calculation.

RESULTS

Between January 2012 to December 2017, 182 patients were included. Upon 20 potentially prognostic factors recorded, 10 were kept, including clinical, biological and imaging factors. In the multivariate analysis, the CIEV was influenced by the cumulative intracranial tumor volume (CITV) (coefficient of 1.95, p<.001). The CIEV F-statistic p-value and R square were <10–15 and 0.30, respectively. The ETT was significantly influenced by the CITV (0.31, p<.001) and the extracerebral disease control (-1.58, p=.049). The F-test p-value and R square were <10-10 and 0.25, respectively. No significant linear regression was found for the ER. Residuals were more clinically relevant for the ETT compared to the CIEV.

CONCLUSION

Being significantly influenced by the cumulative brain tumor volume and the extracerebral disease control, the ETT might be a factor to include in future BM works because its strong relationships with confounding factors and its ability to provide robust intra and inter subjects comparisons.

A new method of constructing CD20/CD22 bispecfic antibody fusion proteins with improved direct lymphoma cytotoxicity compared to rituximab

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Background: Anti-CD20 and anti-CD22 monoclonal antibodies (MAbs) have been shown to have antitumor activity in non-Hodgkin’s lymphoma (NHL) patients. Since preclinical and clinical trials also suggested that combining CD20 and CD22 MAbs, which have different mechanisms of action, could improve antitumor activity without a commensurate increase in toxicity, we hypothesized that a therapeutic advantage may be achieved with bispecific MAbs that bind simultaneously to both CD20 and CD22. Methods: A new platform technology, termed the Dock and Lock method (DNL), was successfully applied to produce a trivalent bispecific antibody, named TF3, which comprises two recombinant Fab fragments of hA20 (humanized anti-CD20 MAb; IMMU-106) stably tethered to one recombinant Fab fragment of epratuzumab (humanized anti-CD22 MAb; IMMU-103) via the specific interaction between a dimerization-and-docking domain and an anchoring domain appended to hA20 and epratuzumab, respectively. The cytotoxicity of TF3 was evaluated by cell-based assays using NHL cell lines. Results: TF3 is stable in both human and mouse sera andexhibitsthe samebinding affinity as hA20 IgG or epratuzumab Fab by competitive ELISA. With a 3-day MTT assay, TF3 at 10 nM inhibited 50% and 60% growth of Daudi and Ramos cells, respectively. Further, the observed anti-proliferative activity increased synergistically to >90% in the presence of anti-IgM (0.1 μg/mL). Results from a cell counting assay also demonstrated the ability of TF3 at 1 μM to completely inhibit the growth of Daudi and the potency of TF3 at 1 nM was comparable to that of rituximab at 1 μM under the same experimental conditions, reflecting a 1000-fold enhancement. Conclusions: These findings, to be extended by ongoing in vivo studies, suggest that the new DNL platform technology for making bispecific antibody fusion proteins provided a CD20/CD22 binding protein that is significantly more potent than rituximab in an in vitro NHL direct cytotoxicity assay.

[Table: see text]

Reticulocyte transferrin receptor (TfR) expression and contribution to soluble TfR levels

BACKGROUND AND OBJECTIVES

Transferrin receptor (TfR) expression in erythroid cells is regulated by a number of factors, including iron status and erythropoietin (Epo) stimulation. However, the impact of these factors on reticulocyte TfR expression in vivo has never been studied. A soluble form of TfR (sTfR) is present in serum in proportion to the mass of cellular TfR. Although sTfR shedding by reticulocytes and erythroblasts has been demonstrated in vitro, the contribution of reticulocyte TfR to serum sTfR has never been evaluated in vivo.

DESIGN AND METHODS

We measured directly the total number of reticulocyte TfR in normal rats of different age and iron status, as well as in animals experiencing various conditions and treatments aimed at altering erythropoietic activity and iron status, including rHuEpo therapy, hemolytic anemia, phlebotomies, hypertransfusions, thiamphenicol-induced red cell aplasia or inflammation. In addition, we examined the impact of repeated hypertransfusions with normal, reticulocyte-poor and reticulocyte-rich blood on serum sTfR levels.

RESULTS

The number of TfR molecules per reticulocyte was around 50,000 in young rats but was around 100,000 in older animals. These values remained constant in most conditions and in particular were not influenced by iron supplementation or iron overload. However, functional iron deficiency as well as rHuEpo therapy resulted in increased reticulocyte TfR expression. In addition, TfR numbers in reticulocytes were elevated in the early phase of recovery after acute hemolysis or red cell aplasia but normalized soon after. Hypertransfusion experiments clearly demonstrated that reticulocytes can contribute substantially to sTfR levels in vivo.

INTERPRETATION AND CONCLUSIONS

TfR numbers are regulated in vivo by the same factors as in vitro, in particular iron deficiency and erythropoietin stimulation. Circulating reticulocytes contribute significantly to serum sTfR levels.

Cessation of intensive treatment with recombinant human erythropoietin is followed by secondary anemia

Little information is available on the evolution of erythropoiesis after interruption of recombinant human erythropoietin (rHuEpo) therapy. Iron-overloaded rats received 20 daily injections of rHuEpo. During treatment, reticulocytes, soluble transferrin receptor (sTfR), and hematocrit increased progressively. This was accompanied by a substantial expansion of spleen erythropoiesis but a decrease in the bone marrow. Five weeks after treatment, rats developed a significant degree of a regenerative anemia. Erythropoietic activity, as assessed by reticulocytes, sTfR, erythroid cellularity, iron incorporation into heme, and the number of erythroid colonies, was severely depressed 3 weeks after cessation of rHuEpo. This was followed by regeneration of erythroblasts and reticulocytes at weeks 6 to 7 post-Epo, but erythroid progenitors recovered only partially by that time. The anemia was definitely corrected 2 months after cessation of rHuEpo treatment. Serum Epo levels remained elevated for several weeks, but the sensitivity of marrow erythroid precursors to Epo was preserved. No rat antibodies to rHuEpo were detected, and serum from post-Epo animals did not exert any inhibitory activity on erythropoiesis. In conclusion, after cessation of intensive rHuEpo therapy, there was a strong inhibition of erythropoietic activity with secondary anemia followed by late recovery. This was not due to antibodies or other soluble inhibitory factors, a defect in endogenous Epo production, or a loss of sensitivity to Epo. This may rather represent intrinsic erythroid marrow exhaustion, mostly at the level of erythroid progenitors but also at later stages of erythropoiesis.

The effect of recombinant human erythropoietin on platelet counts is strongly modulated by the adequacy of iron supply

The effect of recombinant human erythropoietin (rHuEpo) on megakaryopoiesis remains controversial. Treatment with rHuEpo in renal failure patients has been associated with a slight elevation of platelet counts. In animal studies, high doses of rHuEpo produced an increase of platelet counts followed by a gradual return to normal after 7 to 15 days or even a substantial degree of thrombocytopenia. However, because iron deficiency is also known to be associated with thrombocytosis, (functional) iron deficiency during rHuEpo could be contributing to these observations. We investigated the impact of iron supply on changes in platelet counts induced by rHuEpo. Rats were either fed normal food (normal rats) or received 1% carbonyl iron for 2 weeks or 3 months, as well as during the experiment, to achieve iron supplementation or overload, respectively. Rats of all three categories then received daily intravenous injections of rHuEpo (10, 50, or 150 U) or normal saline (0 U) for 20 days. With 0 to 10 U rHuEpo, platelets remained stable. In normal rats receiving 50 to 150 U rHuEpo, platelets increased to 120% to 140% of baseline at 4 to 12 days to level off at 120% at 16 to 20 days. This response was less sustained in splenectomized animals. Iron-supplemented rats receiving 50 to 150 U rHuEpo also increased platelets initially, but the peak was at day 4, followed by a gradual return to baseline and even a moderate thrombocytopenia later on. Iron-overloaded rats receiving 50 to 150 U rHuEpo also had increased platelets at day 4, but the duration of platelet increase was shorter, and they experienced a more pronounced degree of thrombocytopenia in proportion to the dose of rHuEpo. Because the early elevation of platelets was of larger magnitude than hematocrit changes, it is unlikely that it could be accounted for by shrinkage of plasma volume. Because it was observed in all three iron conditions, there appears to be some direct positive effect of rHuEpo on platelet production. However, after this transient effect, expanded erythropoiesis appears to exert a negative impact upon platelet production. Secondary thrombocytopenia was not related to splenic pooling, and its very slow correction after cessation of rHuEpo therapy is not compatible with changes in platelet survival. Rather, it is consistent with stem cell competition between erythroid and megakaryocytic development. However, this secondary thrombocytopenia is masked by (functional) iron deficiency in rats not receiving an adequate iron supply from food or stores.

Soluble and cell-associated transferrin receptor in lung cancer

The expression of transferrin receptor (TfR) has been identified in many malignant tumours. In lung cancer, lymphoma and breast cancer, it has been shown that the expression of TfR correlates with tumour differentiation, probably implying some prognostic value. A soluble form of TfR (sTfR) in human serum has been shown to be proportional to the number of cellular TfRs. Based on these data we examined the utility of measuring sTfR in the serum and bronchoalveolar lavage (BAL) fluid of patients with lung cancer (n = 32) and patients with chronic obstructive pulmonary disease (n = 22). BAL fluid was centrifuged to separate the supernatant from the cellular component. Cells were lysed in a detergent and cell-associated TfR was measured by enzyme-linked immunosorbent assay (ELISA) and expressed as ng 10(-6) cells in this cellular component. There was no difference in serum sTfR between the cancer and chronic obstructive pulmonary disease (COPD) groups. A higher level of cell-associated TfR was found in BAL of non-small-cell lung cancer patients than in COPD patients (P = 0.01). The calculated number of TfR molecules per cell in BAL correlated positively with the percentage of macrophages in BAL (P < 0.0001), suggesting that cell-associated TfR in BAL originates primarily from macrophages in this fluid. No correlation existed between BAL cell-associated TfR and tumour size, nodal status, the presence of metastases and serum sTfR. BAL cell-associated TfR was negatively correlated with BAL supernatant neuron-specific enolase (NSE) (P = 0.01). A combination of BAL supernatant NSE and cell-associated TfR detected lung cancer with a sensitivity of 91%, a specificity of 59% and positive and negative predictive values of 81% and 71% respectively. In conclusion, BAL cell-associated TfR may help in the differential diagnosis of lung cancer vs pneumonia.

Isolation and cloning of JTAP-1: a cathepsin like gene upregulated in response to V-Jun induced cell transformation

The oncogenic potential of Jun in chicken embryo fibroblasts (CEF) varies depending on its structure. V-Jun, which has a number of structural differences from c-Jun is highly transforming and tumorigenic. C-Jun however, is only weakly transforming and is not tumorigenic. We have used this difference in oncogenic potential between v-Jun and c-Jun to screen for downstream target genes associated with the v-Jun induced transformed phenotype. We describe here the identification, cloning and characterization of one of these genes, JTAP-1. JTAP-1 is consistently overexpressed 7 to 10-fold in CEF transformed by v-Jun compared with c-Jun overexpressing or normal CEF. This pattern of expression suggests that JTAP-1 is associated with the transformed phenotype. DNA and amino acid homology search analysis revealed that JTAP-1 shares a high degree of similarity with over 100 cysteine proteases from a variety of species and is likely the chicken homolog of cathepsin O. Analysis of expression of JTAP-1 in CEF overexpressing other oncogenes including v-Ha-ras, v-Src, c-Fos, and Myc revealed that it's overexpression is unique to v-Jun transformed cells. Thus, JTAP-1 is likely a specific target of v-Jun overexpression and not simply a consequence of cell transformation.

Quantitative assessment of erythropoiesis in haemodialysis patients demonstrates gradual expansion of erythroblasts during constant treatment with recombinant human erythropoietin

Recombinant human erythropoietin (rHuEpo) has been shown to be effective in correcting the anaemia of chronic renal failure. It has been reported that reticulocytes as well as erythroid progenitors increase within 1-2 weeks, with no further elevation beyond this time interval. However, the erythroblast pool is quantitatively the most important compartment of erythropoiesis, and the rate, extent and duration of the expansion of erythropoietic activity in response to rHuEpo is not known. Treatment with rHuEpo was given to 64 patients i.v. thrice weekly after haemodialysis. The effect of rHuEpo was obvious from the early elevation of reticulocyte counts, but much of this increase was due to a rapid output of shift reticulocytes which levelled off after a few weeks. Serum transferrin receptor (TfR), a quantitative measure of erythropoiesis, increased progressively over 6 weeks to reach a plateau phase at about twice baseline values. The Hct increased progressively and continued to rise steadily after the TfR plateau was reached. The speed and extent of the expansion of erythropoietic activity correlated with the later haematological response to rHuEpo. When rHuEpo was discontinued, erythropoietic activity returned progressively to baseline values, to rise again gradually when treatment was resumed. Part of the Hct increase was also due to haemoconcentration. The results indicate that changes in the various erythroid compartments vary considerably in intensity and speed, and that the erythroblast compartment in particular is slow to respond to modifications in the erythropoietin stimulus.

Effect of recombinant human erythropoietin on platelets in patients with anemia of renal failure: correlation of platelet count with erythropoietic activity and iron parameters

We examined the effect of treatment with rHuEpo on platelet counts in 61 hemodialysis patients and correlated them with changes in erythropoietic activity, iron status and inflammation. Platelets (10(9)/1) increased from 220 +/- 80 to 245 +/- 102 after 14 days and stabilized at that level up to day 90 (p < 0.0001). The increment was similar in complete or partial responders but was not observed in failures. Serum transferrin receptor (sTfR, a measure of total erythropoiesis) and Het rose much more progressively, but relative platelet increments correlated with relative increases in sTfR and Hct. Relative platelet increments correlated inversely with relative changes of SeFe or transferrin saturation, but not with their absolute values, nor with baseline ferritin or its progressive decrease. Although baseline platelet count was 12% higher in patients with inflammation and correlated with serum haptoglobin, relative increases were similar in patients with or without inflammation. In conclusion, rHuEpo produced a clinically minor but consistent elevation of platelet counts. These modifications were not related primarily to modifications in iron stores, functional iron deficiency, or inflammation, but paralleled the expansion of erythropoietic activity. The results suggest that rHuEpo has a small positive effect on platelet production, but it cannot be ruled out that this could be partially mediated through functional iron deficiency.

Early prediction of response to recombinant human erythropoietin in patients with the anemia of renal failure by serum transferrin receptor and fibrinogen

Recombinant human erythropoietin (rHuEpo) has been shown to be effective in correcting the anemia of chronic renal failure, but the dose needed may be variable. The reason for this variation is not known, but several factors could be involved, such as iron deficiency, inflammation, aluminum intoxication, hyperparathyroidism, blood losses, or marrow dysfunction. Treatment with rHuEpo was given intravenously thrice weekly after hemodialysis to 64 consecutive unselected patients with the anemia of chronic renal failure. The starting dose was 50 U/kg/dose, which was increased to 75 and 100 U/kg/dose if no response was observed after 1 and 2 months of treatment. After a minimum follow-up of 6 months, response was evaluated as early (hematocrit [Hct] > or = 30% before 3 months) or late (Hct > or = 30% after 3 months) response, or failure (target Hct not attained). We examined the value of various laboratory parameters (baseline values and early changes) as predictors of response to rHuEpo. The best prediction by pretreatment parameters only was obtained with baseline serum transferrin receptor (TfR) (< or > or = 3,500 ng/mL) and fibrinogen (< or > or = 4 g/L): 100% response rate when both parameters were low, versus only 29% when they were both high, and versus 67% when one was low and the other high. When the 2-week TfR increment was greater than 20%, the response rate was 96%. When TfR increment was less than 20%, the response rate was 100% when baseline TfR and fibrinogen were low, 12% when fibrinogen was elevated, and 62% when fibrinogen was low but baseline TfR high. The predictive value of baseline TfR and fibrinogen and of the 2-week increment of TfR was confirmed by life table analysis and stepwise discriminant analysis. Major reasons for failure or late response were identified and included subclinical inflammation, iron deficiency, functional iron deficiency, marrow disorders, hemolysis, bleeding, and low Epo dose. We conclude that response to rHuEpo can be predicted early by pretreatment fibrinogen and TfR, together with early changes of TfR levels. These prognostic factors illustrate the importance of the early erythropoietic response, subclinical inflammation, and functional iron deficiency. Early recognition of a low probability of response in a given patient could help identify and correct specific causes of treatment failure to hasten clinical improvement and avoid prolonged ineffective use of an expensive medication.

Mixed connective tissue disease presenting myasthenia gravis

We herein describe a 41-year-old female patient with an association of myasthenia gravis (MG) with anti-acetylcholine receptor (AcR) antibody, mixed connective tissue disease (MCTD) and Sjögren's syndrome (SjS). We reviewed the reported association of MG and MCTD, systemic lupus erythematosus, progressive systemic sclerosis, polymyositis and dermatomyositis, and SjS. Since we could find only two patients who fulfilled the diagnostic criteria for MCTD in the previous literature, we concluded that the association of MG and MCTD is rare. We also discuss the coexistence of SjS as one of the underlying pathological conditions for the association of MG and various connective tissue diseases including MCTD.

In vivo viral and cellular Jun complexes exhibit differential interaction with a number of in vitro generated 'AP-1- and CREB-like' target sequences

A direct comparison of the relative DNA-binding capabilities of in vivo Jun-containing complexes derived from overexpression of the highly transforming viral Jun (VJ-1 CEF), the weakly transforming chicken cellular Jun (CJ-3 CEF) or background endogenous Jun (RCAS CEF) was assessed by gel mobility-shift assays using a synthetic oligonucleotide containing the consensus sequence TGACTCA (consensus AP-1). Chicken embryo fibroblasts (CEFs) expressing background c-Jun levels (RCAS CEF) contain almost undetectable levels of c-Jun but retain significant DNA-binding activity with two distinct complexes capable of binding specifically to the consensus AP-1 site. CEFs overexpressing either v-Jun or c-Jun contain these same two complexes and, while showing marked increases in Jun protein levels, do not exhibit any increase in DNA binding or transcriptional activation activity, suggesting that much of the overexpressed protein is inactive. Gel-shift assays performed in the presence of a Jun-specific antibody revealed a reduction in binding by both complexes, suggesting that each contains Jun or a Jun cross-reactive protein. Antibodies specific for Jun B, c-Fos, Fos B and CREB failed to interact with either complex. However, antibody specific for Fra-2 caused a slight supershift, suggesting that one or both complexes may contain Fra-2. Gel-shift competition assays with 16 'AP-1- and CREB-like' target sequences revealed that, within each cell type, the two protein complexes varied in their ability to recognize the mutant target sequences. These results clearly indicate differences in potential target recognition by each specific in vivo complex, and suggest that each may preferentially bind its own subset of target DNAs. In addition, a comparison of binding by individual complexes derived from CEFs overexpressing v-Jun and c-Jun also revealed differences in target recognition. Thus, in vivo complexes formed by overexpression of v-Jun and c-Jun vary in their ability to recognize and bind to a number of 'AP-1- and CREB-like' target sequences. This has important implications with regard to the mechanisms involved in cell transformation by v-Jun.

Erythropoiesis in multiple myeloma: defective red cell production due to inappropriate erythropoietin production

We investigated the pathophysiology of erythropoiesis in 62 patients with multiple myeloma and examined whether it would establish a rational basis for the treatment of their anaemia with recombinant human erythropoietin. Erythropoietin (Epo) production was evaluated by serum levels and erythropoiesis was quantitated by serum transferrin receptor (TfR) levels, both assessed relative to the degree of anaemia. Instead of the expected stimulation of erythropoiesis in response to anaemia, haematocrit correlated positively with marrow erythropoietic activity, indicating that the mechanism of anaemia was primarily defective red cell production. Erythropoiesis decreased and anaemia worsened significantly with advancing clinical stage. 25% of the patients had inadequate Epo production and this proportion increased to 50% in stage 3. Inappropriate Epo production was seen in 60% of patients with renal impairment but was also observed in a number of patients with normal renal function. Erythropoiesis correlated strongly with the adequacy of Epo production, particularly in advanced disease. We conclude that most myeloma patients have defective red cell production even in the absence of massive marrow infiltration and that inappropriate Epo production contributes to their anaemia.

Repair-resistant mutation in Neurospora

Chronic UV treatment produces severalfold fewer mutations in Neurospora conidia than does the same total dose of acute UV. Experiments were designed to determine the conditions required for chronic UV mutagenesis. Measurement of the coincidence frequency for two independent mutations revealed the existence of a subset of cells which are mutable by chronic UV. Analysis of forward mutation at the mtr locus showed that the genetic alterations produced by chronic UV were virtually all point mutants, even though the assay system could detect alterations or deletions extending into neighboring genes. A significant fraction of the mutants produced by acute UV were multigenic deletions. The size of the dose-rate effect (acute UV mutation frequency divided by chronic UV mutation frequency) was compared for several different mutation assay systems. Forward mutations (recessive lethals and mtr) gave values ranging from four to nine. For events which were restricted to specific molecular sites (specific reversions and nonsense suppressor mutations), there was a wider range of dose-rate ratios. This suggests that chronic UV mutation may be restricted to certain molecular sequences or configurations.

Pitfalls of prenatal diagnosis of 21-hydroxylase deficiency congenital adrenal hyperplasia

Hormonal measurements and HLA genotyping of amniotic fluid at midgestation correctly predicted the postnatal diagnosis of congenital adrenal hyperplasia (CAH) in 29 of 32 fetuses at risk. Of these 29, 7 were predicted to have prenatal-onset classical 21-hydroxylase deficiency (21-OH def) based on elevated amniotic fluid 17-hydroxyprogesterone (17-OHP) and delta 4-androstenedione (delta 4-A) levels. These 7 fetuses and their index cases were ultimately proven to have salt-wasting classical 21-OH def. Of 5 who were HLA typed, the genotype was identical to the index case in 4; in one, HLA prediction was not possible, because the parents shared identical HLA antigens. Normal amniotic fluid 17-OHP and delta 4-A levels in the remaining 22 fetuses predicted that they were not affected with classical CAH. These children have been clinically asymptomatic to date or proven biochemically not to have classical or nonclassical CAH. Of the 22 fetuses, 11 were predicted by HLA genotyping to be homozygous normal or heterozygous for 21-OH def. In 3 of the 32 fetuses, prenatal diagnosis was incorrect. In one, the fetus was predicted to have CAH based on HLA identity to the index case. However, amniotic fluid 17-OHP and delta 4-A were normal, and the fetus was normal. The index case of this family did not have CAH, but was a normal child. Thus, amniotic fluid hormone levels accurately predicted a normal fetus, while HLA genotyping was not relevant in prenatal diagnosis because the index case was unaffected. The second fetus was predicted to be affected on the basis of HLA genotyping and to be unaffected based on normal amniotic fluid 17-OHP and delta 4-A. During infancy, this female infant had postnatal-onset nonclassical CAH. The index case in this family, presumed to have classical simple virilizing CAH, was later diagnosed to have nonclassical CAH. Thus, in nonclassical CAH, hormonal measurement of 17-OHP and delta 4-A is not useful in prenatal diagnosis; only HLA genotyping of the fetus is valuable. In the third case, the fetus was predicted to be a heterozygote by HLA genotyping and to be unaffected by hormonal measurement. Postnatally, at age 2 7/12 yr, the male child was found to have classical simple virilizing CAH and to be HLA-B-DR identical to his brother (index case) who also has classical simple virilizing CAH.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurospora crassa temperature-sensitive mutant apparently defective in protein synthesis

A temperature-sensitive mutant of Neurospora was isolated which appeared to be defective in the initiation of protein synthesis. The defect in mutant 34Cts was apparently due to a single gene mutation, and was recessive in heterokaryons. Conidial germination was normal and hyphal growth was nearly so in the mutant at 20 C, but both were greatly inhibited at 35 C. After 15 min at 35 C there was a reduced rate of protein synthesis, followed by decreases in ribonucleic acid and deoxyribonucleic acid synthesis. The percentage of ribosomes in polysomes declined at 35 C and the average size of polysomes decreased. Because the decrease in protein synthesis, it was believed that some part of the translational system may be affected by the mutation. Mutant 34Cts was given the designation psi-1.