Are there some Kabbalistic concepts that are studied today in Jewish circles that originate from Christianity /Christian theology?
Has there been any study of the relationship between the two, and the direction of influence?
Gershom Scholem and other scholars have linked the development of Kabbalah in the 13th century to earlier pre-christian Gnostic ideas. To quote from the "Origins of Kabbalah":
Certain fundamental characteristics of Gnosticism are nevertheless fully congruent with the kind of mysticism we find in the Merkabah writings: the possession of a knowledge that cannot be acquired by ordinary intellectual means but only by way of a revelation and mystical illumination; the possession of a secret doctrine concerning the order of the the celestial worlds and the liturgical and magical-theurgical means that provide access to it.
... The central teaching of Gnosticism consists of methodical instructions for the ascent of the soul from the earth through the spheres of the hostile planet-angels and rulers of the cosmos to its divine home. ... The fact remains that precisely these ideas were affirmed in the heart of an esoteric discipline within the Jewish tradition.
There are many concrete examples of shared Gnosticism, such as the concept of the רקיע שביעי, and the ogdoad.