Best I can think of is DNA.

You said it yourself that your vampires feed mostly on the blood of other animals much like a vampire bat, but vampire bats are in simply for the nutrients in the blood (which aren't all that many, requiring the animal to feed regularly and one of the reasons they'll die if they go longer than 3 days without a proper blood meal), so out of the "bat" we can see it must be related to something other than nutrients.

Therefore your vampires need something else specifically from humans and which no other species has. My best guess for why they'd need it? Your vampires need the human genome itself.

According to this forensic site from the University of Arizona:

Blood is an excellent source of human DNA. DNA is present in white blood cells of humans, but not red blood cells which lack nuclei. A dime-sized spot of blood, approximately 50 µl in volume, is enough DNA for a typical VNTR analysis.

This fact, coupled with the fact that vampires are a result of genetic mutations that evolved alongside humans lead me to the following conclusion: for whatever reason, at the cost of enhanced senses and abilities when compared to normal humans, vampires have an unstable genome, and rely on human DNA to maintain their bodily functions, so, similarly to how rotifers incorporate the genes of plants, fungi and bacteria they eat to ensure their genetic diversity and remain capable of thriving and ensuring genetic diversity despite reproducing via cloning, your vampires incorporate the human DNA found from the white blood cells ingested with the human blood, using it as a way to repair certain parts of their own DNA, which are almost identical to the same parts found in normal human DNA but also seem to "degrade" over time for unknown reasons (be it mutation, deletion or any other process), these parts cease to code certain enzymes vital for the vampire's survival, and need to be replaced by a healthy counterpart copied from normal human DNA every once in a while, in a process similar to what's seen with CRISPR/CAS-9. If a vampire fails to consume human DNA, these structures will degrade to the point it can no longer relay the codes its meant, resulting in the lack of production of certain proteins and enzymes vital for their survival, culminating in their bodies shutting down for good.

As to how they would perform this separation of components before sending what's useless for digestion, I'd suggest that the vampires have a special stomach divided in 2 chambers, a smaller chamber in which the white blood cells are separated for posterior DNA "extraction" by the vampire's natural CRISPR/CAS9 system and a main chamber where what's not needed by the vampire in its current state is digested as it would be in a "normal" stomach.

Best I can think of is DNA.

You said it yourself that your vampires feed mostly on the blood of other animals much like a vampire bat, but vampire bats are in simply for the nutrients in the blood (which aren't all that many, requiring the animal to feed regularly and one of the reasons they'll die if they go longer than 3 days without a proper blood meal), so out of the "bat" we can see it must be related to something other than nutrients.

Therefore your vampires need something else specifically from humans and which no other species has. My best guess for why they'd need it? Your vampires need the human genome itself.

According to this forensic site from the University of Arizona:

Blood is an excellent source of human DNA. DNA is present in white blood cells of humans, but not red blood cells which lack nuclei. A dime-sized spot of blood, approximately 50 µl in volume, is enough DNA for a typical VNTR analysis.

This fact, coupled with the fact that vampires are a result of genetic mutations that evolved alongside humans lead me to the following conclusion: for whatever reason, at the cost of enhanced senses and abilities when compared to normal humans, vampires have an unstable genome, and rely on human DNA to maintain their bodily functions, so, similarly to how rotifers incorporate the genes of plants, fungi and bacteria they eat to ensure their genetic diversity and remain capable of thriving and ensuring genetic diversity despite reproducing via cloning, your vampires incorporate the human DNA found from the white blood cells ingested with the human blood, using it as a way to repair certain parts of their own DNA, which are almost identical to the same parts found in normal human DNA but also seem to "degrade" over time for unknown reasons (be it mutation, deletion or any other process), these parts cease to code certain enzymes vital for the vampire's survival, and need to be replaced by a healthy counterpart copied from normal human DNA every once in a while, in a process similar to what's seen with CRISPR/CAS-9. If a vampire fails to consume human DNA, these structures will degrade to the point it can no longer relay the codes its meant, resulting in the lack of production of certain proteins and enzymes vital for their survival, culminating in their bodies shutting down for good.

As to how they would perform this separation of components before sending what's useless for digestion, I'd suggest that the vampires have a special stomach divided in 2 chambers, a smaller chamber in which the white blood cells are separated for posterior DNA "extraction" by the vampire's natural "genetic editing" system and a main chamber where what's not needed by the vampire in its current state is digested as it would be in a "normal" stomach.

Best I can think of is DNA.

You said it yourself that your vampires feed mostly on the blood of other animals much like a vampire bat, but vampire bats are in simply for the nutrients in the blood (which aren't all that many, requiring the animal to feed regularly and one of the reasons they'll die if they go longer than 3 days without a proper blood meal), so out of the "bat" we can see it must be related to something other than nutrients.

Therefore your vampires need something else specifically from humans and which no other species has. My best guess for why they'd need it? Your vampires need the human genome itself.

According to this forensic site from the University of Arizona:

Blood is an excellent source of human DNA. DNA is present in white blood cells of humans, but not red blood cells which lack nuclei. A dime-sized spot of blood, approximately 50 µl in volume, is enough DNA for a typical VNTR analysis.

This fact, coupled with the fact that vampires are a result of genetic mutations that evolved alongside humans lead me to the following conclusion: for whatever reason, at the cost of enhanced senses and abilities when compared to normal humans, vampires have an unstable genome, and rely on human DNA to maintain their bodily functions, so, similarly to how rotifers incorporate the genes of plants, fungi and bacteria they eat to ensure their genetic diversity and remain capable of thriving and ensuring genetic diversity despite reproducing via cloning, your vampires incorporate the human DNA found from the white blood cells ingested with the human blood, using it as a way to repair certain parts of their own DNA, which are almost identical to the same parts found in normal human DNA but also seem to "degrade" over time for unknown reasons (be it mutation, deletion or any other process), these parts cease to code certain enzymes vital for the vampire's survival, and need to be replaced by a healthy counterpart copied from normal human DNA every once in a while, in a process similar to what's seen with CRISPR/CAS-9. If a vampire fails to consume human DNA, these structures will degrade to the point it can no longer relay the codes its meant, resulting in the lack of production of certain proteins and enzymes vital for their survival, culminating in their bodies shutting down for good.

Best I can think of is DNA.

You said it yourself that your vampires feed mostly on the blood of other animals much like a vampire bat, but vampire bats are in simply for the nutrients in the blood (which aren't all that many, requiring the animal to feed regularly and one of the reasons they'll die if they go longer than 3 days without a proper blood meal), so out of the "bat" we can see it must be related to something other than nutrients.

Therefore your vampires need something else specifically from humans and which no other species has. My best guess for why they'd need it? Your vampires need the human genome itself.

According to this forensic site from the University of Arizona:

Blood is an excellent source of human DNA. DNA is present in white blood cells of humans, but not red blood cells which lack nuclei. A dime-sized spot of blood, approximately 50 µl in volume, is enough DNA for a typical VNTR analysis.

This fact, coupled with the fact that vampires are a result of genetic mutations that evolved alongside humans lead me to the following conclusion: for whatever reason, at the cost of enhanced senses and abilities when compared to normal humans, vampires have an unstable genome, and rely on human DNA to maintain their bodily functions, so, similarly to how rotifers incorporate the genes of plants, fungi and bacteria they eat to ensure their genetic diversity and remain capable of thriving and ensuring genetic diversity despite reproducing via cloning, your vampires incorporate the human DNA found from the white blood cells ingested with the human blood, using it as a way to repair certain parts of their own DNA, which are almost identical to the same parts found in normal human DNA but also seem to "degrade" over time for unknown reasons (be it mutation, deletion or any other process), these parts cease to code certain enzymes vital for the vampire's survival, and need to be replaced by a healthy counterpart copied from normal human DNA every once in a while, in a process similar to what's seen with CRISPR/CAS-9. If a vampire fails to consume human DNA, these structures will degrade to the point it can no longer relay the codes its meant, resulting in the lack of production of certain proteins and enzymes vital for their survival, culminating in their bodies shutting down for good.

As to how they would perform this separation of components before sending what's useless for digestion, I'd suggest that the vampires have a special stomach divided in 2 chambers, a smaller chamber in which the white blood cells are separated for posterior DNA "extraction" by the vampire's natural CRISPR/CAS9 system and a main chamber where what's not needed by the vampire in its current state is digested as it would be in a "normal" stomach.