Prescription drug use is prevalent during pregnancy, yet there is limited knowledge about maternal-fetal safety and efficacy of this drug use because pregnant individuals have historically been excluded from clinical trials. Underrepresentation has resulted in a lack of data available to estimate or predict fetal drug exposure. Approaches to study fetal drug pharmacology are limited and must be evaluated for feasibility and accuracy. Anatomic and physiological changes throughout pregnancy fluctuate based on gestational age and can affect drug pharmacokinetics (PK) for both mother and fetus. Drug concentrations have been studied throughout different stages of gestation and at or following delivery in tissue and fluid biospecimens. Sampling amniotic fluid, umbilical cord blood, placental tissue, meconium, umbilical cord tissue, and neonatal hair present surrogate options to quantify and characterize fetal drug exposure. These sampling methods can be applied to all therapeutics including small molecule drugs, large molecule drugs, conjugated nanoparticles, and chemical exposures. Alternative approaches to determine PK have been explored, including physiologically based PK modeling, in vitro methods, and traditional animal models. These alternative approaches along with convenience sampling of tissue or fluid biospecimens can address challenges in studying maternal-fetal pharmacology. In this narrative review, we 1) present an overview of the current understanding of maternal-fetal drug exposure; 2) discuss biospecimen-guided sampling design and methods for measuring fetal drug concentrations throughout gestation; and 3) propose methods for advancing pharmacology research in the maternal-fetal population.

This review highlights strategies to integrate dose optimization into premarketing drug development and discusses the underlying statistical principles. Poor dose optimization can have negative consequences for patients, most commonly because of toxicity, including poor quality of life, reduced effectiveness because of inability of patients to stay on current therapy or receive subsequent therapy because of toxicities, and difficulty in developing combination regimens. We reviewed US Food and Drug Administration initial approvals (2019-2021) of small molecules and antibody-drug conjugates for oncologic indications to determine the proportion with a recommended dosage at the maximum tolerated dose or the maximal administered dose, to characterize the use of randomized evaluations of multiple dosages in dose selection, to describe the frequency of dose modifications at the recommended dosage, and to identify case examples that highlight key principles for premarket dose optimization during drug development. Herein, we highlight major principles for dose optimization and review examples of recent US Food and Drug Administration approvals that illustrate how investigation of dose- and exposure-response relationships and use of randomized dose trials can support dose optimization. Although there has been some progress, dose optimization through randomized dose evaluation in oncology trials is not routinely conducted. Dose optimization is essential to ensure that patients receive therapies which maximize efficacy while minimizing toxicity.

Duocarmycins are a class of DNA minor-groove-binding alkylating molecules. For the past decade, various duocarmycin analogues have been used as payloads in the development of antibody-drug conjugates (ADCs). Currently, more than 15 duocarmycin-based ADCs have been studied preclinically, and some of them such as SYD985 have been granted Fast-Track Designation status. Nevertheless, progress in duocarmycin-based ADCs also faces challenges, with setbacks including the termination of BMS-936561/ MDX-1203. In this review, we discuss issues associated with the efficacy, pharmacokinetic profile, and toxicological activity of these biotherapeutics. Furthermore, we summarize the latest advances in duocarmycin-based ADCs that have different target specificities and linker chemistries. Evidence from preclinical and clinical studies has indicated that duocarmycin-based ADCs are promising biotherapeutics for oncological application in the future.

The objectives of the current study were to determine the effects of supplementing a blend of probiotic bacteria (Provida Calf, MB Nutritional Sciences, Lubbock, TX) on the pathophysiological response to an oral Salmonella enterica serotype Typhimurium challenge in neonatal Jersey calves. Twenty-four Jersey bull calves within 24 h of birth were acquired from a local calf ranch, blocked by total serum protein and initial body weight, and randomly assigned to 1 of 3 treatments (n = 8). Calves were assigned to either (1) Control (CON); base milk replacer, (2) Control + Salmonella Typhimurium (CON+ST); base milk replacer and challenged with Salmonella Typhimurium on d 7; or (3) Provida Calf probiotics + Salmonella Typhimurium (PRO+ST); same milk replacer supplemented with a proprietary blend of Lactobacillus casei and Enterococcus faecium strains and challenged with Salmonella Typhimurium on d 7. The PRO+ST calves were supplemented for the first 3 d with 2 × 1010 cfu/d and then with 2 × 109 cfu/d for the remainder of the study. The CON+ST and PRO+ST calves were each challenged with approximately 5 × 106 cfu of Salmonella Typhimurium (ATCC# 14028), which was a mild challenge that did not cause scours in the calves. Peripheral blood samples were collected on d 0, 7, 10, 14, and 21 and analyzed for hematology; serum was collected and analyzed for haptoglobin, glucose, and urea N. Rectal temperatures were collected daily from d 6 to 21, when all calves were killed, so that persistent colonization of Salmonella Typhimurium and histomorphology of both the duodenum and ileum could be determined. Serum haptoglobin and urea N concentrations were increased among CON+ST on d 10. In contrast, the peak rectal temperature on d 10 in PRO+ST calves was 40.4°C, which was greater than that for CON and CON-ST (38.9°C and 39.7°C, respectively). The neutrophil percentage in peripheral circulation in PRO+ST calves was 55.4%, which was greater than that for CON and CON+ST (34.8 and 41.8%, respectively). Seven of the 8 PRO+ST calves had elevated neutrophil percentages on d 10 compared with d 7, whereas 4 of the 8 CON+ST calves had reduced neutrophil percentages on d 10 compared with d 7. Villus height-to-crypt depth ratios in the duodenum were greater among CON and PRO+ST calves, being 1.38, 0.84, and 1.43 for CON, CON+ST, and PRO+ST, respectively. In the ileum, the PRO+ST calves had greater villus height-to-crypt depth ratios than both the CON and CON+ST calves (1.64, 1.53, and 2.43 for CON, CON+ST, and PRO+ST, respectively). These data indicate that supplementing neonatal calves with the blend of probiotic bacteria used in the current study can influence the pathophysiological response to a mild enteric Salmonella Typhimurium challenge.

The study objective was to determine if a combined weaning and transportation stress model affected performance, antibody, endocrine, or hematological responses to modified-live virus (MLV) or killed virus (KV) respiratory vaccination in beef steers. In total, 48 calves (Day 0 BW = 226 ± 6.2 kg) from a single origin were used in a 2 × 2 factorial to evaluate main effects of stress model, vaccine type, and their interaction, resulting in four treatments (n = 12/treatment) including non-stress control (C) with KV (CKV), C with MLV (CMLV), stress model implementation (S) with KV (SKV), and S with MLV (SMLV). The C calves were weaned at the origin ranch on Day −37 and transported 472 km to the study site on Day −21 to allow acclimation. The S calves were weaned on Day −3, transported 460 km to a research facility on Day −2, held overnight, and transported 164 km to the study site on Day −1 to mimic the beef cattle marketing process. Vaccines were administered on Day 0 and KV was revaccinated on Day 14. The animal was the experimental unit and dependent variables were analyzed using PROC MIXED with repeated measures (day). A stress model effect (p = 0.01) existed for DMI from Day 0 to Day 7 with greater DMI for C (6.19 vs. 4.64 kg/day) when compared to S. The MLV groups had reduced (p = 0.05) ADG from Day 0 to Day 56, compared to KV. There was a vaccine type × day (p < 0.01) interaction with increased (p ≤ 0.01) PI3V- and IBRV-specific antibody titers for KV on Day 21; conversely, MLV had increased (p ≤ 0.01) BVDV titers on Days 14, 28, 35, 42, 49, and 56. Increased (p ≤ 0.05) BRSV titers were observed in a stress model × day (p < 0.01) interaction for S on Days 21, 28, 36, and 42; however, C exceeded S in BVDV-specific antibody concentration on Days 21, 28, and 49. A day effect (p < 0.01) was observed for serum haptoglobin with the greatest (p < 0.01) concentration on Day 3. Serum cortisol concentration was greater (p ≤ 0.04) for C vs. S on Days −2, 0, 1, 3, and 5. Total leukocytes were decreased for C vs. S on Days 0, 1, 3, 5, 7, 14, and 21 (p ≤ 0.02). A reduction (p ≤ 0.04) in total leukocytes was observed for MLV on Days 5, 7, and 14 vs. KV. Neutrophils and neutrophil:lymphocyte were markedly increased (p ≤ 0.01) for S on Day −2, whereas neutrophils were decreased (p ≤ 0.01) on Days 1 and 21 for S. Monocytes were decreased on Days 1, 5 and 7 for MLV (p ≤ 0.04) and Days −2 to 14 for S (p ≤ 0.03). Eosinophils were reduced (p = 0.007) for S vs. C on Day −2, yet a distinct rebound response (p = 0.03) was noted for S on Day 0. The results indicate that S and MLV vaccination more profoundly induced immunomodulation in beef calves.

Treatment of triple-negative breast cancer (TNBC) is a challenge to oncologists. Currently, the lack of effective therapy has fostered a major effort to discover new targets and therapeutics to combat this disease. The recepteur d'origine nantais (RON) receptor has been implicated in the pathogenesis of TNBC. Clinical studies have revealed that aberrant RON expression is crucial in regulating TNBC malignant phenotypes. Increased RON expression also has prognostic value for breast cancer progress. These features provide the rationale to target RON for TNBC treatment. In this review, we discuss the importance of RON in TNBC tumorigenesis and the development of anti-RON antibody-drug conjugates (ADCs) for clinical application. The findings from preclinical studies lay the foundation for clinical trials of this novel biotherapeutic for TNBC therapy.

Advanced epithelial cancers such as gastric, lung, and pancreatic tumors are featured by invasive proliferation, distant metastasis, acquired chemoresistance, and tumorigenic stemness. For the last decade, molecular-targeted therapies using therapeutic antibodies, small molecule kinase inhibitors and immune-checkpoint blockades have been applied for these diseases with significant clinical benefits. Nevertheless, there is still a large gap to achieve curative outcomes. MET (mesenchymal-epithelial transition protein), a receptor tyrosine kinase, is a tumorigenic determinant that regulates epithelial cancer initiation, progression, and malignancy. Increased MET expression also has prognostic value for cancer progression and patient survival. These features provide the rationale to target MET for cancer treatment. In this review, we discuss the importance of MET in epithelial tumorigenesis and the development of antibody-based biotherapeutics, including bispecific antibodies and antibody-drug conjugates, for clinical application. The findings from both preclinical and clinical studies highlight the potential of MET-targeted biotherapeutics for cancer therapy in the future.

Advanced colorectal adenocarcinoma (CRAC), featured by distinctive histopathological appearance, distant organ metastasis, acquired chemoresistance, and tumorigenic stemness is a group of heterogeneous cancers with unique genetic signatures and malignant phenotypes. Treatment of CRAC is a daunting task for oncologists. Currently, various strategies including molecular targeting using therapeutic monoclonal antibodies, small molecule kinase inhibitors and immunoregulatory checkpoint therapy have been applied to combat this deadly disease. However, these therapeutic modalities and approaches achieve only limited success. Thus, there is a pharmaceutical need to discover new targets and develop novel therapeutics for CRAC therapy. MET and RON receptor tyrosine kinases have been implicated in CRAC pathogenesis. Clinical studies have revealed that aberrant MET and/or RON expression and signaling are critical in regulating CRAC progression and malignant phenotypes. Increased MET and/or RON expression also has prognostic value for CRAC progression and patient survival. These features provide the rationale to target MET and RON for clinical CRAC intervention. At present, the use of small molecule kinase inhibitors targeting MET for CRAC treatment has achieved significant progress with several approvals for clinical application. Nevertheless, antibody-based biotherapeutics, although under clinical trials for more than 8 years, have made very little progress. In this review, we discuss the importance of MET and/or RON in CRAC tumorigenesis and development of anti-MET, anti-RON, and MET and RON-dual targeting antibody-drug conjugates for clinical application. The findings from both preclinical studies and clinical trials highlight the potential of this novel type of biotherapeutics for CRAC therapy in the future.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers with poor prognosis and high mortality. Molecular aberrations associated with PDAC pathogenesis and progression have been extensively investigated. Nevertheless, these findings have not been translated into clinical practice. Lack of therapeutics for PDAC treatment is another challenge. Recent application of molecularly targeted and immunoregulatory therapies appears to be disappointing. Thus, discovery of new targets and therapeutics is urgently needed to combat this malignant disease. The RON receptor tyrosine kinase is a tumorigenic determinant in PDAC malignancy, which provides the rationale to target RON for PDAC treatment. In this review, we summarize the latest evidence of RON in PDAC pathogenesis and the development of anti-RON antibody-drug conjugates for potential PDAC therapy. The finding that anti-RON antibody-drug conjugates show efficacy in preclinical animal models highlights the potential of this novel class of anti-cancer biotherapeutics in future clinical trials.

The objective was to determine the effect of replicating and non-replicating vaccine antigens administered to acutely or chronically stressed beef calves on hematologic and endocrine responses. A total of 48 crossbred beef steers (d 0 BW = 226 ± 6.2 kg) from a single ranch origin were used in a 2 × 2 factorial to evaluate main effects of stress, vaccine type and their interaction; resulting in 4 treatments (n = 12/treatment) consisting of acute stress with killed virus vaccination (ACUKV), ACU with modified-live virus vaccination (ACUMLV), chronic stress with KV (CHRKV), and CHR with MLV (CHRMLV). The ACU treatments were weaned at their origin ranch on d -37 and transported 472 km to the study site near Canyon, TX on d -21 to allow acclimation. The CHR treatments were weaned on d -3, transported 460 km to a facility near Lubbock, TX on d -2, and relocated 164 km to the study site on d -1. Vaccine treatments were administered on d 0 and KV was revaccinated on d 14. Animal was experimental unit and dependent variables were analyzed using PROC MIXED with repeated measures (d). Hematological variables were determined from whole blood collected on d -2, 0, 1, 3, 5, 7, 14, and 21 via automated hemocytometer. Cortisol concentration was determined using ELISA from serum collected on d -2, 0, 1, 3, 5, and 7. Total leukocytes were not different on d -2 (P = 0.66), but were lesser for CHR vs. ACU on d 0, 1, 3, 5, 7, 14 and 21 (P ≤ 0.02). Vaccine type also affected total leukocytes; leukocytes were decreased for MLV on d 5, 7, and 14 (P ≤ 0.04) compared to KV. Neutrophils (2.01 vs. 3.83 K/µL) and neutrophil:lymphocyte (0.27 vs. 0.67) were markedly increased (P < 0.001) for CHR on d -2; conversely, neutrophils were decreased (P ≤ 0.007) on d 1 and 21 for CHR. Monocytes were decreased on d 1, 5 and 7 for MLV (P ≤ 0.04) and d -2 to 14 for CHR (P≤0.03). Eosinophils were reduced (P = 0.007) for CHR (0.097) vs. ACU (0.176 K/µL) on d -2; however, a rebound response (P = 0.03) was noted on d 0 such that eosinophils were 0.288 and 0.160 K/µL for CHR and ACU, respectively. Serum cortisol was greater (P ≤ 0.04) for ACU on d -2 to 5, suggesting suppression of endocrine activity in CHR over time. Results indicate this CHR stress model and MLV vaccination may have more profoundly induced immunosuppression in beef calves.

The objectives of these studies were to determine the effects of supplementing a blend of anaerobic bacteria on the growth and health of preweaned and immediately postweaned Holstein calves. Holstein calves within 1 d of birth were randomly assigned to 1 of 2 dietary treatments (N = 35). Treatments included a negative Control and MBiotix Calf (BTX) treatment, which was administered in the milk replacer and top-dressed on the starter during the preweaned and immediately postweaned periods, respectively. The BTX treatment dose was 2 × 109 CFU/d of a proprietary blend of Lactobacillus casei and Enterococcus faecium strains; however, during the first 3 d of the study, the BTX calves were given a 10× dose. The study was conducted in 3 periods (n = 20 Control and n = 15 BTX). Calves were individually housed and fed between 250 and 350 g depending on the period of a 22% CP and 20% fat milk replacer twice daily at 0730 and 1630. Calves had ad libitum access to a calf starter and water. Calves were individually housed until they were weaned at 56 d when they were grouped by treatment for an additional 28 d. Peripheral blood samples were collected on d 0, 7, 21, 56, 70, and 84, and analyzed for hematology. Data were analyzed as a repeated measures ANOVA with treatment, time, and treatment × time as the fixed effects and period as a random effect. Calf nested within treatment was the subject of the repeated statement. Data are reported as Control vs. BTX, respectively. There was a treatment × time interaction (P = 0.001) on calf starter intake during the preweaned period, whereas BTX calves began to consume more starter during the fourth week of life, and the difference in starter intake was different (P ≤ 0.05) during the sixth to eighth week of life. BTX calves were consuming more starter at weaning (1.065 vs. 1.305 ± 0.141 kg/d; P = 0.025). Further, the BTX calves had greater ADG during the 84 d observation period (0.701 vs. 0.883 ± 0.079 kg/d; P = 0.016). There were no treatment or treatment × time effects on hematocrit percentage (34.3 vs. 35.9 ± 1.98%; P ≥ 0.235). Further, there were no treatment or treatment × time effects (P ≥ 0.178) on any hematological variable. These data indicated that supplementing MBiotix Calf improved calf starter intake and average daily gain during the preweaned and immediate postweaned periods.

0099 In silico identification of natural product inhibitors of Brucella abortus threonyl-tRNA synthetase. M. Li, N. Zheng, F. Wen, Y. Zhang, S. Li, S. Zhao, and J. Wang, Ministry of Agriculture Laboratory of Quality & Safety Risk Assessment for Dairy Products (Beijing), Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, China, Ministry of Agriculture–Milk and Dairy Product Inspection Center (Beijing), Beijing, China, State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, China.

The objectives of the study were to determine if supplementing milk replacer with Safmannan (SM) and ActiSaf (AS) would affect calf growth and health throughout the preweaned and immediate postweaned periods. The study was performed over 67 d, with 39 Holstein bull calves. Calves were housed in individual pens in an environmentally controlled barn, and were provided ad libitum access to a texturized calf starter and water, as well as offered 350 g of milk replacer solids, 22% CP and 20% fat, at 0700 and 1600 from d 0 to 56. Calf starter and water refusals were recorded daily and intakes calculated. Calves were randomly assigned to treatments that included CON, milk replacer with no added supplements; SM, milk replacer with 5 g SM/calf/d; and SM + AS, milk replacer with 2 g SM/calf/d and 3 g AS/calf/d. Individual BW was measured on d 0, 21, 42, 56, and 67. Blood samples were collected and analyzed for hematology on d 10, 28, and 56; while plasma and whole blood were collected and analyzed for plasma haptoglobin concentrations, neutrophil surface expression of CD62L, and neutrophil phagocytosis and oxidative burst capacity to an environmental E. coli on d 0, 10, 28, and 56. All data were reported as CON, SM, and SM + AS, respectively. The LSMeans with various superscripts differ (P ≤ 0.05). Individual calf starter intake did not differ over the entire study, although from 0 d to 21 d, calves receiving the SM + AS supplement consumed more starter (0.025a, 0.034ab, 0.074b ± 0.018 kg/d; P < 0.05). Neither ADG (0.63, 0.68, 0.69 ± 0.054 kg/d; P = 0.699), nor feed:gain (1.74, 1.74, 1.73 ± 0.070 kg/kg; P = 0.990) differed among treatments. Total leukocyte counts were greater in the CON calves on d 10 than the other treatments (14.2a, 9.2b, 11.1b ± 1.2 106/mL; P < 0.05) and was lower in the SM calves on d 28 than the CON and SM + AS treatments (10.4a, 7.9b, 10.6a ± 0.87 106/mL; P < 0.037). Neutrophil surface expression of CD62L was greatest in SM calves when compared with CON calves (92,772a, 110,441b, 94,526ab ± 5334 mean fluorescence intensity; P = 0.052). Additionally, there were treatment × time interactions on neutrophil phagocytosis and oxidative burst P ≤ 0.024), whereas SM calves had greater percentages of neutrophils phagocytizing and producing an oxidative burst on d 28. These data suggest that both yeast supplementation strategies may influence the health of high-risk, preweaned Holstein calves.

The objective of this study was to determine the effects of OmniGen-AF (OG) and Provia 6086 (PV) on the performance and health of preweaned and immediately postweaned Holstein calves. Holstein calves within 1 d of birth were randomly assigned to one of four dietary treatments (N = 80). The study was conducted in two consecutive periods with 40 calves/period (n = 10 calves/treatment/period). Dietary treatments were given in both the milk replacer and calf starter. Treatments were arranged and analyzed as a 2 × 2 factorial with OG and PV as the main fixed effects. Diets were formulated to supply approximately 10 g/d of OG and 2 billion CFU/d of PV if calves were consuming milk only or 1.36 kg of calf starter only. Calves were housed in an enclosed barn and fed 275 g of a 22% CP and 20% fat milk replacer daily at 0730 and 1630. Calves had ad libitum access to calf starter and water. The quantity of water and starter offered as well as refused was recorded and adjusted daily for approximately 10% orts. Calves were individually housed until they were weaned at 56 d when they were grouped within treatment with four calves/pen for an additional 28 d. There were no treatment or treatment × time differences on starter intake during either the preweaned (P ≥ 0.111) or postweaned (P ≥ 0.297) periods. Additionally, there were no treatment or treatment × time differences (P ≥ 0.500) in ADG during either the preweaned (0.593 ± 0.096 kg/d) or postweaned (0.845 ± 0.096 kg/d) periods. The surface expression of CD14 on peripheral blood monocytes decreased (P ≤ 0.001) with increased calf age; however, there were no treatment or treatment × time differences (P ≥ 0.339). Similarly, there were no treatment or treatment × time differences (P ≥ 0.316) on the surface expression of CD62L on peripheral blood neutrophils. There was an OG × PV × time interaction (P = 0.018) in peripheral blood neutrophil counts, whereas there was a tendency (P = 0.089) for the Control and OG + PV to have reduced neutrophils when compared with OG and PV calves at 21 d. Lastly, there were no treatment × time differences (P ≥ 0.430) on hematocrit percentages; however, there was a significant time effect (P = 0.001), whereas hematocrits were elevated at 14 and 21 d. These data indicate that OmniGen-AF and Provia 6086 supplementation during the preweaned and immediate postweaned periods did not influence growth performance, leukocyte, or hematological measures in these Holstein calves.

The objective of this study was to determine the effects of supplementing a Saccharomyces cerevisiae fermentation product prototype (Prototype) on the pathophysiological response during a combined viral-bacterial respiratory challenge. Holstein steer calves (126.5 ± 6.11kg; N = 16) were completely randomized to treatments including 0 (CON) or 20 g/head/d of Prototype (n = 8). Calves were housed in open, dry lot corrals with four calves per pen (2 pens/treatment). Calves were offered ad libitum access to a 50:50 total mixed ration of a commercially available 16% CP pelleted calf grower and 18% CP chopped alfalfa hay. Treatments were top dressed for 30 d. Orts were measured daily and the quantity of feed was adjusted for approximately 10% orts. Calves were moved to individual stanchions (2.13 × 0.76 cm) in an enclosed barn, fitted with rectal temperature monitoring devices, and allowed 24 h adaptation before initiating the respiratory challenge. All calves were challenged with 1.5 × 108 PFU·mL–1·nostril–1 of bovine herpesvirus-1 cooper strain at –72 h using a mucosal atomizer and with 106 CFU of M. haemolytica (MH) intratracheal at 0 h. Blood samples were collected via jugular venipuncture at –96, –72, –48, –24, 0, 6, 24, 48, 72, 120, 168, and 240 h relative to the MH challenge. Total leukocytes counts tended (P = 0.063) to be greater at 24 h among CON steers. Neutrophil:lymphocyte also tended to be greater (P ≤ 0.095) at 24 and 72 h among CON steers. Monocyte phagocytosis of an environmental Escherichia coli tended (P = 0.056) to be greater in steers fed the Prototype at 24 h. Neutrophil oxidative burst to an environmental Escherichia coli tended (P = 0.071) to be greater at 6 h and was greater (P = 0.011) at 168 h among steers fed the Prototype. However, monocyte oxidative burst tended (P = 0.052) to be greater among CON at 72h. Neutrophil L-selectin did not differ between treatments (P = 0.515). Neither serum haptoglobin concentrations (P = 0.773) nor rectal temperature (P = 0.985) differed between treatments. These data demonstrate that the Saccharomyces cerevisiae fermentation product prototype may influence some acute leukocyte responses during a viral-bacterial respiratory challenge, but did not have strong influences on measures of inflammation or disease.

The objective of this study was to determine the dose response effects of supplementing Saccharomyces cerevisiae fermentation product prototype on leukocyte functionality and ex vivo cytokine production during a dexamethasone (DEX) challenge. Holstein steers (125.1 ± 8.16 kg; N = 32) were assigned to treatments including 0, 20, 40, or 60 g/head/d of prototype (n = 8). Calves were housed for 21 d in dry lot corrals with four calves per pen (2 pens/treatment). Calves were offered ad libitum access to a 50/50 TMR of a commercially available 16% crude protein pelleted grower and 18% CP chopped alfalfa hay. Treatments were top dressed. The quantity of feed offered and orts were measured daily. After the 21 d adjustment to diets, calves were jugularly catheterized and moved into individual stations (2.13 × 0.76 cm) in an environmentally controlled barn and allowed 48 h to adapt before the first DEX injection. Blood samples were collected at –24, –6, 0, 6, 12, 18, 24, 48, and 72 h relative to the first DEX injection. DEX was administered via jugular catheter at 0.1 mg/kg BW at 0, 6, and 12 h. Peripheral blood neutrophil (PMN) concentrations increased (P < 0.001) at 6 h and remained elevated through 72 h in all steers. Neutrophil L-selectin and PMN and monocyte (MONO) oxidative burst (OB) and phagocytosis (PHAG) of an environmental Escherichia coli decreased (P < 0.059) at 6 h in all steers. L-selectin returned to baseline at 72 h while OB and PHAG failed to return to baseline by 72 h. Total leukocyte counts (P < 0.001) and PMN concentrations (P = 0.001) increased linearly with prototype dose. PMN L-selectin concentrations did not differ (P = 0.684) among treatments. Oxidative burst intensity in PMN (P = 0.025) and MONO (P = 0.003) increased linearly with prototype dose at 72 h, as well as in MONO PHAG intensity (P = 0.004) at 6 h. The percentage of PMN (P = 0.012) and MONO (P = 0.013) that were both PHAG and OB positive increased linearly with prototype at 72 h. Ex vivo whole blood lipopolysaccharide stimulated TNF-α concentrations was greater (P = 0.026) in prototype steers than control steers at –24 h. Overall, these data demonstrate that the dexamethasone challenge induced severe leukocyte dysfunction, and prototype supplementation influenced plasma neutrophil concentrations and may have increased recovery of neutrophil and monocyte function.