Fine-tuned long-acting interleukin-2 superkine potentiates durable immune responses in mice and non-human primate.

BACKGROUND: Recombinant human interleukin-2 (rhIL-2, aldesleukin) is Food and Drug Administration approved for the treatment of metastatic melanoma and renal cell carcinoma and has achieved durable response in a subset of patients. However, its utility as an immunotherapeutic drug is limited by undesirable activation of immune suppressive regulatory T cells (Tregs) and a short half-life requiring frequent high dose administration, leading to unacceptable toxicities. We have engineered MDNA11, a long-acting IL-2 superkine, to overcome these limitations by (1) modifying receptor selectivity in favor of anti-cancer immune cells to increase therapeutic efficacy and (2) fusion to human albumin to extend the pharmacokinetic (PK) profile, circumventing the need for frequent dosing. METHODS: MDNA11 was evaluated using in vitro and in vivo studies including: binding analyses to measure receptor affinity, IL-2 pathway signaling, PK studies in mice, and efficacy studies in syngeneic tumor models as single agent and in combination with immune checkpoint inhibitors. Finally, the safety and pharmacodynamic profile of MDNA11 was assessed in non-human primate (NHP). RESULTS: Binding studies with MDNA11 demonstrated increased affinity for IL-2Rß (CD122) and no binding to IL-2Rα (CD25). As a result, MDNA11 exhibits reduced/limited Treg stimulation while triggering an enhanced activation of natural killer and naïve CD8 T cells compared with rhIL-2. When administered to animals with pre-established tumors, MDNA11 controlled tumor growth in a monotherapy setting and in combination with anti-PD1 or anti-CTLA4 to induce durable tumor clearance with a once weekly dosing regimen. In a NHP model, MDNA11 was well tolerated while triggering durable and potent immune responses including expansion of lymphocytes without significant effect on Tregs and eosinophils, the latter been linked to an increased risk of vascular leak syndrome. CONCLUSION: MDNA11 is a next generation long-acting IL-2 immunotherapeutic with a highly favorable pharmacodynamic profile that translates to a strong therapeutic efficacy in preclinical tumor models and a strong and durable immune response in NHP.

HBOC-201 vasoactivity in a phase III clinical trial in orthopedic surgery subjects--extrapolation of potential risk for acute trauma trials.

BACKGROUND: Vasoactivity has hampered progress of hemoglobin-based oxygen carriers (HBOCs) due to concern for adverse blood pressure responses and secondary complications. A recent formulation, highly polymerized HBOC-201 (Biopure, Cambridge, MA), has been found to be less vasoactive than prior less polymerized formulations, and to improve outcome in animal models of hemorrhagic shock (HS) compared with standard resuscitation fluids. HBOCs are envisioned to have life- saving potential for severe trauma patients for whom death due to HS is common despite transport to level I trauma centers. As part of a benefit:risk analysis for a proposed clinical trial of HBOC-201 in patients with traumatic HS, we analyzed data from a previous phase III clinical trial of this HBOC that involved orthopedic surgery patients, for vasoactivity and related effects, with focus on patients more representative of the trauma population. STUDY DESIGN: In a previous phase III study involving orthopedic surgery patients, HEM-0115, consented/stabilized patients were randomized to receive HBOC-201 (N = 350) (up to ten 30 g Hb units) or red blood cells (RBC) (N = 338) (up to 9 units) at the first transfusion decision. Systolic blood pressure (SBP) responses, key system and individual adverse events (AEs) and serious adverse events, and cardiac biomarker elevation incidences, were compared in the overall population and subpopulations with stable trauma, hypotension, and with age stratification (Student's t and Fisher's exact tests, significance p < 0.05). RESULTS: Mild to moderate peak SBP responses were common in HBOC-201 subjects and more common than with RBC in the overall population (mean, 60.8 years old), but less frequent in HBOC-201 subjects with stable trauma, younger age (<50 years old), and hypotension, in whom group differences were narrowed. SBP Delta responses were more common with HBOC-201 than RBC in the overall population, but not in subjects with stable trauma and <50 year olds, in whom response rates were lower. In the overall population, AEs were more common than with RBC in most systems (also, hypertension and stroke); only cardiac system serious adverse events were more common with HBOC-201. In contrast, there were few significant group differences in stable trauma, hypotensive, and <70 and especially <50-year-old subjects, in whom AE incidences were generally lower. A disproportionate number of key AEs occurred in elderly subjects. Troponin (but not CK-MB) elevation was more frequent with HBOC-201 than RBC in the overall population but not in <50 year olds, and was not associated with acute coronary syndrome (ACS) or death. CONCLUSIONS: Our limited HEM-0115 safety analysis shows that key potentially vasoactivity-related adverse safety signals were more frequent with HBOC-201 than RBC in older patients undergoing orthopedic surgery with rapid access to safe blood transfusions. That incidences of these safety signals were generally lower and group differences narrowed in subpopulations with stable trauma, hypotension, and younger age, suggests an acceptable safety profile in younger acute trauma populations, especially in settings where rapid access to safe blood transfusions is unavailable; confirmation in controlled clinical trials is urgently warranted.

HBOC-201 as an alternative to blood transfusion: efficacy and safety evaluation in a multicenter phase III trial in elective orthopedic surgery.

BACKGROUND: The ability of hemoglobin based oxygen carrier-201 (HBOC-201) to safely reduce and/or eliminate perioperative transfusion was studied in orthopedic surgery patients. METHODS: A randomized, single-blind, packed red blood cell (PRBC)-controlled, parallel-group multicenter study was conducted. Six hundred eighty-eight patients were randomized to treatment with HBOC-201 (H, n = 350) or PRBC (R, n = 338) at the first transfusion decision. Primary endpoints were transfusion avoidance and blinded assessment [Mann-Whitney estimator (MW)] of safety noninferiority. Groups were compared directly and by paired/matching group analyses predicated on a prospectively defined dichotomy [treatment success (HH) vs. failure (HR)] in the H arm and an equivalently defined dichotomy [3 (R3+) units PRBC] in the R arm, based on need (moderate vs. high) for additional oxygen carrying capacity. RESULTS: A total of 59.4% of patients in the H arm avoided PRBC transfusion. Adverse events (8.47 vs. 5.88), and serious adverse events (SAEs) (0.35 vs. 0.25) per patient were higher in the H versus R arms (p < 0.001 and p < 0.01) with MW = 0.561 (95 CI 0.528-0.594). HH versus R3- had identical (0.14) serious adverse events/patient and a MW = 0.519 (95% confidence limit 0.481-0.558), whereas the incidence was higher (0.63 vs. 0.47) for HR versus R3+ with a MW = 0.605 (95% confidence limit 0.550-0.662). Age (>80 years), volume overload and undertreatment contributed to this imbalance. CONCLUSION: HBOC-201 eliminated transfusion in the majority of subjects. The between arms (H vs. R) safety analysis was unfavorable and likely related to patient age, volume overload, and undertreatment and was isolated to patients that could not be managed by HBOC-201 alone. However, patients <80 years old with moderate clinical need may safely avoid transfusion when treated with up to 10 units of HBOC-201.

Innate immune response after resuscitation with hemoglobin-based oxygen carrier and recombinant factor VIIA in uncontrolled hemorrhagic shock in a swine model.

BACKGROUND: Rapid resuscitation with oxygen-carrying fluids is critically important in hemorrhagic shock (HS) combat casualties in remote areas where blood is not available. Hemoglobin-based oxygen carrier-201 (HBOC-201) has been shown to increase survival and reduce immune activation following HS in animal models. Recombinant factor VIIa (rfVIIa), a systemic hemostatic agent, is Food and Drug Administration approved for use in acute hemorrhage in hemophilic patients. The combination of HBOC-201 and rfVIIa may form the basis of a prospective multifunctional blood substitute and provide benefits in the rapid restoration of hemostasis, decreased inflammation and improved survival of HS combat casualties. In the present study, we evaluated innate immune responses in a swine model of uncontrolled HS following resuscitation with HBOC-201 +/- rfVIIa. MATERIALS: Thirty-two pigs underwent uncontrolled hemorrhage/liver crush injury, followed by resuscitation with five doses of HBOC-201 or HBOC + rfVIIa (90 microg/kg, or 180 microg/kg, or 360 microg/kg) and simulated 4 hours hospital arrival. Immune parameters were evaluated by flow cytometry and enzyme-linked immunosorbent assay. RESULTS: Survival differences to 72 hours of animals resuscitated with HBOC, HBOC + rfVIIa (90), (180), and (360) were not statistically significant and resulted in survival of 25%, 63%, 63% and 50%, respectively. At the prehospital phase all groups exhibited minimal immunomodulation, characterized by stable CD4/CD8 ratio, marginal increase of apoptosis and insignificant fluctuations of adhesion markers; increase of plasma cytokines was comparable across all groups, except tumor necrosis factor-alpha, that was significantly elevated in the HBOC group. CONCLUSION: HBOC-201 + rfVIIa triggered minimum immune activation in an uncontrolled HS swine and there was a nonsignificant survival benefit.

The effects of decreasing low-molecular weight hemoglobin components of hemoglobin-based oxygen carriers in swine with hemorrhagic shock.

BACKGROUND: Some hemoglobin-based oxygen carriers (HBOCs) improve outcome in animal models of hemorrhagic shock (HS) in comparison with standard asanguinous resuscitation fluids. Nevertheless, concern about intrinsic vasoactivity, linked in part to low-molecular weight (MW) hemoglobin (Hb), has slowed HBOC development. We assessed the impact of decreasing the low-MW Hb component of bovine HBOC on vasoactivity in severe HS. METHODS: Anesthetized invasively monitored swine were hemorrhaged 55% blood volume and resuscitated with bovine HBOC containing 31% (31 TD [HBOC-301]), 2% (2 TD [HBOC-201]), or 0.4% (0.4 TD) low-MW Hb. Pigs received four 10 mL/kg infusions over 60 minutes, hospital arrival was simulated at 75 minutes, organ blood flow (BF) was evaluated by microsphere injection, and monitoring was continued for 4 hours followed by complete necrotic evaluation. RESULTS: There were few differences between 2 TD and 0.4 TD. Thirty-one TD pigs had higher systemic and pulmonary blood pressure (BP), systemic vascular resistance index, and pulmonary artery wedge pressure, compared with 2 TD or 0.4 TD (p < 0.01); however, pigs in all groups had at least mildly elevated BP. Transcutaneous tissue oxygenation, base excess, and mixed venous oxygen saturation were similar across groups; lactate and methemoglobin were highest with 0.4 TD (p < 0.03). There were no group differences in BF. Over time, myocardial BF increased and hepatic BF decreased in all groups (for 31 TD, p < 0.05); renal BF was unchanged in all groups. There were no group differences in heart, lung, or liver histopathology, and survival. CONCLUSIONS: Although purification from 31% to 2% low-MW Hb content significantly decreased vasoactive responses, further purification to 0.4% had no additional clinically measurable effects in severe HS. If further diminution in HBOC vasoactivity is desired for use in HS, additional technical approaches may be required.

Bovine polymerized hemoglobin versus Hextend resuscitation in a swine model of severe controlled hemorrhagic shock with delay to definitive care.

To compare the efficacy of low-volume resuscitation with bovine polymerized hemoglobin (HBOC-201) versus hetastarch (HEX) in an intermediate severity combat-relevant hemorrhagic shock swine model with a simulated delay to hospital care. Twenty-four anesthetized pigs were hemorrhaged 55% estimated blood volume in conjunction with a 5-min rectus abdominus crush. At 20 min, pigs were resuscitated with 10 mL/kg of HBOC-201 or HEX or nothing (NON); resuscitated pigs received additional infusions (5 mL/kg) at 30, 60, 120, or 180 min if hypotension or tachycardia persisted. Pigs were monitored for a 4-h "prehospital" period. At 4-h, hospital arrival was simulated: surgical sites were repaired, blood, or saline provided, and pigs were recovered from anesthesia. Pigs were monitored for 72 h and then killed for histological evaluation. One hundred percent (8/8) of HBOC-201-, 75% (6/8) of HEX-, and 25% (2/8) of NON-resuscitated pigs survived to 72 h (P = 0.007 overall, HBOC vs. HEX P > 0.05). Mean arterial pressure and mean pulmonary arterial pressure were highest in the HBOC-201 group (P < 0.001), and HR was lowest (P < 0.001). HBOC-201- and HEX-resuscitated pigs had comparable cardiac index and prehospital fluid requirements. HBOC-201 pigs had higher transcutaneous tissue oxygen tension, P < 0.001) and lower urine output (P < 0.001). At simulated hospital arrival, no HBOC-201 pigs required additional fluids or blood transfusion. In contrast, 100% of HEX pigs required blood transfusions (P < 0.01). In this swine model of controlled hemorrhage with low-volume resuscitation and delayed definitive care, HBOC-201 pigs had improved hemodynamics, transcutaneous tissue oxygen tension, and transfusion avoidance compared with HEX.

Immune effects of resuscitation with HBOC-201, a hemoglobin-based oxygen carrier, in swine with moderately severe hemorrhagic shock from controlled hemorrhage.

HBOC-201, a hemoglobin-based oxygen carrier, improved physiologic parameters and survival in hemorrhagic shock (HS) animal models. However, resuscitation from HS and the properties of different fluids influence immune responses. The aim of this study was to determine if HBOC-201 significantly alters immune function in traumatic HS. Anesthetized pigs underwent soft tissue injury, controlled hemorrhage of 40% of blood volume, and resuscitation with HBOC-201 or Hextend, or no resuscitation. Sequential whole-blood samples were collected for analyses of leukocyte differential (hematology analyzer), T-lymphocyte subsets (CD3, CD4, and CD8) (FACS), lymphocyte adhesion marker CD49d (alpha4-integrin) expression (FACS), plasma cytokines-tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-10-(ELISA), and lymphocyte apoptosis (annexin-V/propidium iodide staining) (FACS). Statistical analyses were performed by the mixed procedure. Total WBC counts decreased posthemorrhage in both resuscitation groups. Lymphocyte percentages decreased and PMN percentages increased around 4 h posthemorrhage in all groups. CD3 cells decreased in all groups, but CD4 and CD8 cells decreased only in the resuscitation groups. TNF-alpha levels were not detectable in any groups. IL-6 levels were similar across treatment groups (P > 0.05); however, IL-10 levels were higher in the HBOC group, as early as 1 h posthemorrhage (P = 0.04). Increases in lymphocytic CD49d expression levels and apoptosis occurred only in nonresuscitation and Hextend groups, respectively (P < or = 0.01). In comparison with Hextend, HBOC-201 had no significant adverse or beneficial effects on immune function in this model of moderately severe HS in swine, suggesting that it may be safe as a resuscitation fluid in HS patients.

A hemoglobin-based oxygen carrier, bovine polymerized hemoglobin (HBOC-201) versus hetastarch (HEX) in a moderate severity hemorrhagic shock swine model with delayed evacuation.

OBJECTIVE: To evaluate the efficacy of HBOC-201 for resuscitation of hemorrhagic shock in a swine model incorporating soft tissue injury and delayed evacuation. METHODS: A muscle crush injury and 40% estimated blood volume controlled hemorrhage was completed in 24 Yucatan mini-pigs. Pigs were untreated or resuscitated with HBOC-201 or 6% hetastarch (HEX) at 20 min. Invasive hemodynamics and clinical variables were monitored for 4 h (pre-hospital phase) and subsequent fluid infusions were administered for severe hypotension or tachycardia. Animals were recovered from anesthesia and monitored non-invasively to 72 h (hospital phase). RESULTS: 100% (8/8) of HBOC-201-, 88% (7/8) of HEX-, and 63% (5/8) of non-resuscitated pigs, survived to 72 h (p=0.27). Mean arterial pressure, mean pulmonary arterial pressure and systemic vascular resistance index were higher in HBOC-201 pigs. By 90 min, cardiac index was restored to baseline in the HBOC-201 group and was 1.4-fold greater than baseline in the HEX group. HBOC-201 pigs had lower fluid requirements than HEX pigs (18.8+/-1.8 and 29.9+/-1.1 ml/kg, p<0.001) in the pre-hospital phase and required fewer blood transfusions (1.3+/-1.3 and 9.4+/-0.6 ml/kg, respectively, p<0.001) in the hospital phase. Urine output and blood creatinine were comparable in HBOC-201 and HEX pigs. Tissue oxygenation levels were highest in the HBOC-201 group. CONCLUSIONS: As HBOC-201 restored hemodynamics and tissue oxygenation and decreased fluid requirements, in comparison with HEX, HBOC-201 was at least as efficacious and possibly a superior resuscitative fluid in a military-relevant delayed evacuation hemorrhagic shock swine model.

HBOC-201 improves survival in a swine model of hemorrhagic shock and liver injury.

BACKGROUND: Blunt abdominal trauma that leads to hemorrhagic shock and cardiac arrest is almost always fatal in the prehospital setting. The current study investigated whether a hemoglobin-based oxygen carrier (HBOC-201) could maintain organ viability during an exsanguinating liver injury and allow for prolonged survival. This hypothesis was tested in a large animal model that simulated blunt abdominal trauma with major organ injury. METHODS: Swine underwent a liver crush, laceration and 50 ml/kg initial blood loss. The liver bled at 3 ml/kg per min during the resuscitation phase. No fluid (NF=6), hetastarch (HES=8), or HBOC-201 (HBOC=8) was given during the resuscitation phase. Swine alive 60 min after the initial injury underwent liver repair and 96 h observation. RESULTS: All HBOC swine survived 60 min versus none of the NF or HES swine (P<0.05). All HBOC swine survived 24 h and 7/8 survived 96 h with good functional recovery. CONCLUSIONS: HBOC resuscitation during liver bleeding in a swine model of hemorrhagic shock and liver injury allowed for 96 h survival. No fluid or HES in the same model was fatal.

The pharmacology of tissue oxygenation by biopure's hemoglobin-based oxygen carrier, Hemopure (HBOC-201).

Biopure's hemoglobin-based oxygen carrier, HBOC-201 (Hemopure), enhances oxygen transport by promoting both the convective and diffusive components of transport in the microcirculation. Convective transport is modified by HBOC-201 in three ways; (i) volume expansion promotes organ and tissue perfusion, (ii) the low viscosity of HBOC-201 improves flow to tissues, and (iii) oxygen delivery by HBOC Hb in the plasma is relatively insensitive to mechanisms regulating RBC distribution in the microcirculation. Diffusive oxygen transport is increased by the higher P50 compared with native RBC Hb which increases the off-loading of oxygen to tissues. Oxygen transport is also increased by reducing the diffusional barrier to oxygen transport associated with the plasma, in which oxygen is sparingly soluble. Biopure's HBOC solutions have been shown in vitro and in vivo to take up and off-load oxygen more efficiently than RBC Hb, and when added to blood can increase the efficiency of RBC oxygen transport.

Resuscitation with the hemoglobin-based oxygen carrier, HBOC-201, in a swine model of severe uncontrolled hemorrhage and traumatic brain injury.

The purpose of this investigation was to compare the effects of initial resuscitation with HBOC-201 to that of lactated Ringer (LR) solution in the setting of uncontrolled hemorrhage and traumatic brain injury (TBI). Anesthetized immature swine underwent fluid-percussion TBI and liver laceration. During a 75-min "prehospital phase," the animals were resuscitated with HBOC-201, LR solution, or nothing (NON). Upon "hospital arrival," the animals were provided blood and 0.9% NaCl as needed, and the liver injury was repaired. Surviving animals were killed 6 h after injury. Brain tissue was processed for blood flow, and gross, light microscopic, and immunohistochemical analyses. Mean TBI force (2.6 +/- 0.6 atm) and blood loss (64.4 +/- 3.4 mL/kg) were similar between groups. Six-hour survival was significantly greater in HBOC-201 (8 of 13 [62%]) versus LR solution (1 of 11 [9%]) and NON (1 of 8 [3%]) animals (P < 0.02). Mean arterial pressures, cardiac indices, cerebral perfusion pressures, and brain tissue oxygen tension were significantly greater, and lactate and base deficit were lower in HBOC-201 as compared with LR solution animals. Blood transfusion requirements were reduced in HBOC-201 (3.6 +/- 0.6 mL/kg per survival hour) as compared to 7.1 +/- 1.2 mL/kg per survival hour. Severity of subarachnoid and intraparenchymal hemorrhages was statistically greater in LR solution-treated animals, but these differences were not likely to be clinically significant. There were no differences in glial fibrillary acidic protein and microtubule-associated protein 2. In this model of combined uncontrolled hemorrhage and TBI, initial resuscitation with HBOC-201 resulted in significant improvements in survival and systemic and cerebrovascular physiological parameters, as well as a reduction in transfusion requirements.

Immune effects of decreasing low-molecular weight hemoglobin components of hemoglobin-based oxygen carriers (HBOC) in a swine model of severe controlled hemorrhagic shock.

Hemoglobin-based oxygen carriers (HBOCs) show potential as safe, efficacious, pre-hospital resuscitation fluids. The major criticism of HBOC-201 is its vasoactive property, attributed partially to low-molecular weight (low-MW) tetrameric/dimeric (TD) hemoglobin (Hb) in HBOC solution. Here we sought to determine whether resuscitation with decreasing concentrations of low-MW Hb component of HBOC affects immune responses in hemorrhagic swine. 28 anesthetized swine underwent a soft muscle crush and controlled hemorrhage of 55% blood volume, followed by resuscitation with HBOC containing 31%, 2%, or 0.4% low-MW Hb in four 10 ml/kg infusions at 20, 30, 45 and 60 minutes before hospital arrival at 75 minutes. IL-10, cell activation and adhesion markers and CD4:CD8 ratio remained unchanged in all 3 groups compared to baseline. Leukocyte apoptosis was equally elevated across all groups. Purification from 31% to 0.4% low-MW Hb in HBOC solution did not alter immune effects in a swine model of severe controlled hemorrhagic shock.

Innate immune responses in Swine resuscitated from severe traumatic hemorrhagic shock with hemoglobin-based oxygen carrier-201.

Hemoglobin-based oxygen carrier-201 transports oxygen and improves survival in swine with hemorrhagic shock, but has potential to be immune activating. Herein, we evaluated HBOC-201's immune effects in swine with more severe hemorrhagic shock due to soft tissue injury and 55% blood volume catheter withdrawal over 15 minutes followed by fluid resuscitation at 20 minutes with HBOC-201, Hextend, or no treatment (NON) before hospital arrival. Survival rates were similar with HBOC-201 and Hextend (p > 0.05), but were higher than in (p = 0.007). There were no significant group differences in blood cell count, percentages of leukocyte sub-populations and immunophenotype (CD4:CD8 ratio), adhesion markers expression (neutrophil CD11b; monocyte or neutrophil CD49d) and apoptosis. There was a trend to higher plasma IL-10 in HBOC-201 and groups vs. Hextend. We conclude that in swine with severe controlled HS and soft tissue injury, immune responses are similar with resuscitation with HBOC-201 and Hextend.

Mode of action: yolk sac poisoning and impeded histiotrophic nutrition--HBOC-related congenital malformations.

Rodents form an early inverted yolk sac placenta (invYSP) by apposing the yolk sac to the uterine wall. The invYSP supplies nutrients via histiotrophic nutrition involving pinocytosis of materials from uterine gland secretions, lysosomal degradation, and transfer of the products to the embryo. Interference with histiotrophic trafficking through the invYSP by high-molecular-weight molecules (such as trypan blue) causes malformations and resorptions. Later in gestation, rodents form a definitive chorioallantoic placenta (CAP). By contrast, humans and dogs never develop an invYSP, relying exclusively on the CAP. Given their large size (approximately 250 kD), hemoglobin-based oxygen carriers (HBOC), being developed as blood substitutes, could be expected to interfere with histiotrophic trafficking through the invYSP. During initial toxicity testing, intravenous infusions of HBOC caused pronounced developmental toxicity in rats exposed during the pre-CAP period. Assuming that HBOC interfered with invYSP function, we hypothesized that these findings would not apply to humans or dogs, which lack an invYSP. Subsequent extensive developmental toxicity studies in dogs produced no developmental toxicity after intravenous infusion at the maximum tolerated dose. In view of the existing species-specific placental differences and HBOC's demonstrated, exclusive interference with invYSP histiotrophic nutrition, HBOC is not expected to cause abnormal development in humans or other mammals that do not develop an invYSP.

A hemoglobin based oxygen carrier, bovine polymerized hemoglobin (HBOC-201) versus Hetastarch (HEX) in an uncontrolled liver injury hemorrhagic shock swine model with delayed evacuation.

BACKGROUND: As HBOC-201 improves outcome in animals with hemorrhagic shock (HS), we compared HBOC-201 and HEX (used by U.S. military special operations forces) in a swine model of delayed evacuation and uncontrolled HS. METHODS: Twenty-four Yucatan pigs underwent a grade III liver injury and were resuscitated with HBOC-201, HEX, or no fluid (NON). Additional infusions were given for hypotension or tachycardia. After 4 hours, the liver was repaired; IV fluids and blood transfusions were administered. Pigs were monitored for 72 hours. RESULTS: Survival was 7/8, 1/8, and 1/8 in HBOC-201-, HEX-, and NON-resuscitated pigs, respectively. Compared with HEX, HBOC-201 pigs had higher systemic and pulmonary artery pressures and had comparable cardiac outputs, but were less tachycardic. Transcutaneous tissue oxygenation was restored more rapidly in HBOC-201 pigs, there was a trend to lower lactic acid, and base deficit was less. HBOC-201 pigs had lower fluid requirements, higher urine output, and lower blood loss than HEX pigs. CONCLUSIONS: Despite evidence of vasoactivity, HBOC-201 more effectively stabilized tissue oxygenation, reversed anaerobic metabolism, decreased bleeding, and increased survival in comparison with HEX. If confirmed in clinical trials, these data suggest that for the resuscitation of combat casualties with delayed evacuation and uncontrolled HS due to solid organ injury, HBOC-201 is a superior low-volume resuscitative fluid.